Hi, I'm at a similar stage to you, a bit of reasonably successful experimentation. I've bought a movement from Cousins before (cousinsuk.com) and it was fine, have you tried them? I'm also going to buy an ETA quartz movement from them soon(ish). Plenty of people here don't like them much because they can be difficult to deal with, so caveat emptor. Also one tip is to decide whether you want to buy a sealed version of the movement or not. The price is quite different but the sealed ones are apparently much more 'factory fresh'. For a bit of playing about that may not matter.
Best of luck.