Rumour has it a springer M1A1 thompson is on the way fairly soon, if you don't want to spent hundreds on the base gun (most of which is discarded to make the pulse rifle anyway).
Rumour also has it, the G&P kit from Japan is about to be re-released too, an improved model with stronger shrouds. (the fellows at airsoft atlanta told myself and Derek this)
Toyko Marui makes an excellent electric airsoft thompson that the G&P kit is designed for. The TM costs around $300, and the G&P used to go for around $400 I do believe. Don't quote me. Be aware you will have to purcahse the shorter magazine too, the one that comes with is too long.
Hudson makes a nice PFC replica of the M1A1 as well. This goes for about $700 - $900 all by itself. Sold regularly by modelguns.co.uk
DON"T buy the model 1928, with the charging handle on the top and the boxy upper, like this:
You want the charging handle on the side, and you need these grooves where the upper reciever meets the grip frame for the shroud to fit on. Like so:
Wilco/Dreadnaught-Industries makes a resin and styrene model for the more
skilled builders among us. I recently painted the reciever that comes with the kit in krylon
ultra flat black to give it a nice parkerized look.
The Monsters in Motion version, I believe BEFORE Tom got ahold of it and improved it.
And there is always the ebay classic
chunky funky all resin Pulse Rifle is you really want it, it's still around from time to time.
Hope this helps.