AR riding eh?  Cool.  I am actually building a bike that might fit your description as we speak.  I chose the CS-MB01 From XMCarbonSpeed.  When I was shopping, I wanted a hardtail, but I was looking for something that was a little more forgiving in the rear as I want to run a full carbon seat with no padding and I have an old injury at my L4 disk that I didn't want to aggravate. What gave me the idea to look for something like this was the new BMC Teamlite. It has an elastomer in the seat stays that gives the rear some flex and travel.  The CS-MB01 doesn't have this but it does have a couple of kevlar inserts. What they did with the design is decoupled the top of the stays from the lowers by cutting them on a 45 degree angle and then inserting kevlar housed in a flexible casing in between. I don't believe it will give the travel the BMC gives (claimed 12 to 15mm) but I do think it will soften the harshness just a bit.  I will find out this weekend when I go for my first trail ride on it.

As for price, I am pretty close to your 3K mark in price as well, maybe just a tad under.  Here is what I have:

Frame CS-MB01 - Carbonspeed (Peter @ xmcarbonspeed.com)
Wheels 29 with Novatec hubs - Carbonspeed
Bars - Carbon from Carbonspeed
Seat Post - Carbon from CarbonSpeed
Saddle: G-House all carbon (Selle SMP clone) $25 from Aliexpress (Thanks carbon_dude for the link, I love this thing!)
Fork - Fox 32 Factory SC (Step Cast) very light and got it under $875. Message me for supplier.
Brakes: Hope Tech 3 X2 - Merlin Cycles for about $260.00
Rotors: Hope copies by Snail from AliExpress ($25 for the pair)
Stem: Fun 80mm 7degree from Chain Reaction Cycles (about $25)
Grips: RaceFace Half Nelsons from Chain Reaction Cycles ($20)
Groupset: SRAM GX with 1400 crankset upgrade from r2-bike.com (about $350).
Pedals: I have from another bike.
Tires: Ground Controls 2.3 ($55)

... Just did a running total and I think I'm at $2795.  I have a thread up in this forum and will be updating with more details and pictures over the coming days.  I'm one of the early builds on this particular frameset, so I feel I need to give as much feedback as possible to help others out.  Check there to know more about the build details.

Regardless of what frame and wheels you go with, these component resources should be helpful.  Living in Florida, I was surprised that it was cheaper for me to order the majority of my components from UK and Germany for less than I could find anywhere stateside.... Even with shipping. Just a note on r2-bike.com.  If you are in a region like me where the VAT tax does not apply, make sure to register on their site.  Originally the prices didn't look so good until I registered. Once they had my geographical location, the VAT tax was removed from the pricing.  Just an FYI on that one. 

For those of you following this thread, I went with Hope Tech 3 XC brakes.  Again great advice and info from you guys over in the components area.  I think everything is in transit to me except the fork, but it's coming domestically once the shop receives it, so probably 2-3 days I am thinking.

.... The waiting is the hardest part.... Right Tom Petty? 

Thanks for that input.  X2 with braided hose is what I think I'll do.  Just hope the 5mm hose will route through the frame. I asked Peter about the MB01 and if it would fit, but he didn't know as he has never actually built that model.

Guess I'll be updating you on what happens with that as well.

I'm building the MB01, but was wondering about X2 or E4 brakes.  From what I gather the X2 is more XC geared and weighs a little less.  The E4 is more enduro and has a dual piston caliper at the expense of about 40 grams.  I can afford to go either way and kind of tempted to go E4, but wondering if I just might be over thinking it. Yes, I will be riding mostly in Florida, but on the occasion I am traveling, there might be a few descents. When I was in Kentucky this past summer, some of the road riding to get to the trail had a 2 mile descent.  Again, this will be my first hydraulics, so any advice would be great.

I'm most likely going to order from Merlin.  They have the best prices I could find even though only black.  I wanted Orange since I will have that orange Fox fork and blue accents (grips, and other odds and ends).  But at $80 more for a color from another vendor, I can't justify it. 

As I am getting parts on order and checking my budget, I could potentially squeeze enough for the Hope Tech 3 X2 from Chain Reaction Cycles.  This will be my first set of hydraulics, so I was wondering if it's worth going the extra $120+/- dollars? 

I've watched videos on how to bleed both brakes and it seems the Hope Tech may be easier, and doesn't require any special funnel or other proprietary items.  This would come in handy if I am traveling and don't have that stuff with me. 

Also, they come in colors which is nice.   

Any thoughts on performance and upkeep comparisons?

Just wanted to let everyone know I found a few interesting things with r2-bike.com. 

The site gives you different pricing based on your sign in state.  If you just visit the site and compare the prices and convert Euros to dollars, they don't seem to be any better than many of the other sites.  However, once you login the pricing drops on certain items.

Once I did this, I was able to see about a 57 Euro discount on the group set I was looking at (Gx).  However the brakes t (XT) didn't change much, so I ordered them domestically. 

They shipped the next day and I have my DHL tracking number.  Seems they have better deals on certain manufacturers, but it's worth checking into.

Just and FYI for anyone shopping components....

So I heard back from the guy who owns the bike in the pic that Peter sent out to a few of us (facing to the right with a rigid fork and those funky laced wheels).

Turns out he is happy with the frame. However he feels it could be a little bit stiffer, but he said he is running the 135mm QR instead of a 142 Through Axle.  Also he is almost 200lbs.  I'm only 160, and I ordered the Through Axle, so it will be interesting to see what I find when it arrives.

From the owner of the bike in the pic:
"The frame is good and the ride is soft-ish, I would like it  little stiffer or less comfortable, can`t really tell if those kevlar inserts are making a big difference. With a QR at the rear instead of the thru axel and my weight is 190 pounds so that doesn't do much good for the frame.
This also makes it a bit wobbly in the corners, still much better then my specialized hard rock fully 26”
Im riding it with crank brothers wheels cobalt 2 and a fixed front fork.
The quality of the frame and all other parts is good so is the finishing.
All-in all I`m happy with the bike."

More to come...

Hahahaha!  In the video you said, "Don't have to sell your car..."


... I sold my car and used some of the $$ to buy mine....  But I had enough for the bike and a down payment on a new car.