Hi, Exile,
You indicate you are interested in either a belt-fed semi auto or a belt fed machinegun. In the former, I think there are only three currently on the market, semi-auto clones of the .50 HBM2, .30 M1919, and the German MG.34. All are expensive. There is a wider selection of full-auto, even more expensive.
I am not sure what you mean by a good choice. A full auto Browning M1919 would be hard to beat for endurance and quality. A .50 gives a lot of bang for the buck but is over a buck a bang. Believe me, a belt fed goes through ammo fast, very fast, even in semi-auto.
An M60 would be OK, but the links are a bit harder to come by than Browning links, plus the Browning will work with cloth belts, which the M60 and MG.34/42 will not. An M60 runs, I think, around $10k.
Every once in a while, something exotic, like a Vickers or Maxim or a Russian Maxim comes on the market, but it would be catch as can on those.
Jim