It is a very gratifying experience if you try.
Novatec 711/712 are very light, good and cheap.
Light bicycle can provide you very light rims. Even carbon aero spokes(maybe harder to start with than Pillar or CX-Rays).
So you can end at about 1kg for a wheelset.
I build almost all of my wheels myself and you can indeed build a set for 350-400 EUR that is 1100-1200gr.
I am having trouble buying the Novatec 411-412 hubs from Ali (seems like every seller uses these as some sort of scam...) and they are too expensive to buy in the EU (>200 EUR).
I have now ordered a set of Goldix R180 hubs to build my next MTB wheelset. I hope they have upgraded the ratchet mechanism because I was hesitant to buy Goldix hubs until now because of all the bad reviews...
You can get the Novatec 791-792 hubs very cheap on ali if you wait for the sales. Than you have a 1200 gr wheelset for a little over 300 eur.