I have been researching PCC's for a while now. From what I have seen, a 9mm AR15 and a 9mm Beretta CX4 are two of the best and not terribly expensive. M1 carbines now sell for more than both of these rifles and the cheap ones you can find in Keltec and Highpoint are garbage. I have checked both out and until something better comes alone, the Beretta is the most impressive and can be had for about $550 and cheaper if you shop around. If you get lucky and find one of the Marlin Camp Carbines made years ago those are fun too but you don't see them very often.
As a side note, I have heard rumors of someone making a PCC that takes Glock Mags but I haven't found any creditable info on it yet. Some of the AR15 9mm rifles take Glock mags but I have heard they are hit or miss in quality. It would be fantastic if Glock made one based on the G17 pistol.