I have 5 semi belt feds. A 1919a4, RPD, MG34, M53, and a Maxim. The 1919A4 is a good one to start with. It this the cheapest one to start with, you should be able to find one from $1000-1500. If you go to
www.1919a4.com you can find out all about them It is the one that I have the least amount of problems with. Allied Armorment hasn't had the best rep on that board, I would read up on them before buying one of there guns. There are plenty of other makes out there. The RPD would be a good second. If you go to gunbroker you should be able to find one for $2500-$2600. The M53 (it is the Yugo version of the MG42) are going for around $2500 but some people are having problems with them you can go to
www.mg42.us to find out about them. The one I have shoots good some time and bad the other times, I haven't had a chance to work the kinks out yet. The MG34 is a very nice gun, but it can be picky also. They go for $3500-$4000. The Maxim is a good gun and I haven't had too many problems with it, it is just a pain in the ass to lug around.
I would recomend a 1919A4 for your fist belt fed. You can get them in many diffrent calibers, 7.62x51, 8mm, 30/06, 7.62x54, 7.62x39. But go to the 1919a4 site and read and ask questions there. I built my gun from reading that site (it was the first gun I ever built and it worked). You can ask questions also about the other belt feds out there and most likly someone there will have one and can give you the good and bad on the gun.