Athens Guns. All transfers are FREE. Just do the right thing and spend some cash there for using their services. I bought from Silencershop and filed the form 4 through Athens Guns for free. Didn't need to pay for the Silencershop service either. Athens Guns fills it out based upon what's on the form 3 and gives you a signed copy. Then you mail it to ATF yourself with the check. This was a few months ago, but the form 3 between Silencershop and Athens Guns took 17 days. I remember Silent Industries in Madison had what I was looking for in stock and already form 3'd, but it would have been about $150 more after sales tax, etc.
I think Larry's is $100 for a class 3 transfer. If you buy from them its "free". When I checked they didn't have anything great in stock, but they were pitching their stock as the best products on the market.