A couple of months ago I bought a Prusa Mk 3 3D printer kit, as it generally seems to be considered the best for under $1000. Took quite a while to put it together, as I was doing it in short spurts when I had some free time, and on two or three occasions I had to take parts of it apart when I realized I hadn’t assembled them correctly.
But I got it working over Christmas and it’s printing without many issues; the biggest one is that the filament sometimes gets caught on the spool where one layer has somehow become caught under another, and that’s screwed up a couple of prints so far.
My main advice for assembly would be to read the comments on the online instruction manual, because there’s a lot of information in there that’s useful to prevent you from doing things you shouldn’t.
I also managed to slightly crack one 3D-printed part by tightening a bolt just a little too much, but so far it’s not affected operation. It’s just the duct that directs cooling air from the fan onto the material near the print head, so a slight misalignment probably won’d do much.