What about BCG this one seems well priced from RRA for $110
http://rockriverarms.com/index.cfm?fuseaction=category.display&category_id=377
Those are ok, but, I would opt for a full auto one from any number of places. Check Palmetto State Armory, Joe Bob's Outfitters, Primary Arms, etc. You should be able to score a Premium M16 Full Auto MPT/HP for $119 to $149, which would be much better, in my opinion. I just bought a Spikes ($139) from Joe Bob's, but since I also bought a Joe Bob's upper stripped receiver, it was reduced to $119.
You might even consider this. I bought two here:
Bolt Carrier
Keep watching websites like Palmetto State for sales. They usually have great deals on major holidays. Their Premium M16 Bolt Carriers are $109 when they have a sale. Right now they are $149. So waiting can pay huge dividends, later.
I personally would stay away from their PTAC line of parts, but that is an option for many on a budget.
I also bought a couple of these:
Brownells Bolt Carrier Group They are good to go!
I have also bought three BCM's, 1 Rubber City Armory BCG's, but they ran about $189 to $250. Since I am not a competitive shooter, I have opted for the mid-range BCG's from here on out.