ATM, you can only really save serious money if you go full low budget with direct2consumer-parts from China. I built my TT-X38 with LTWOO er9, Magene powermeter and full carbon wheels + a number of 2nd hand parts (like my Sram cranks, saddle and Vittoria tires) for less than 2.5k EUR. But to do that, you're required to invest A LOT of time researching parts, be prepared to deal with problems when building the bike up and you need to take the risk that customer service and warranty might be troublesome or even more or less non existent.

I mean, there's a GIANT concept store in my city. For not that much more money, I could probably walk in there, grab a bike and come back and have the shop deal with issues, should there be any. But for me, this is also about the journey. I like to come up with the idea of "my dream bike", source all the parts and think every little detail through and then build up something that I couldn't buy anywhere else and that potentially no one else has.

+1 on the garden hose clamp + cheap hacksaw. I've cut 5 steerers like that, 4 carbon, 1 alu. I changed the blade once, probably should have changed it more often. The local DYI store sells blades for very cheap.
Spray water to avoid breathing in the carbon dust. You'll be shocked to see how black the water gets. You definitely don't want to breathe that.
Don't use a pipe cutter on a carbon steerer, you may crush and delaminate the carbon.