Hello, usabaker,
It depends on what you are looking for. Seems the gunbroker and gunauction sites list sporters between $250 and $450 dollars, usually with some hyped-up description which includes words like "rare" and "hard to find."
Realistically, I've seen them in gun-shops for around $100 to $250, with just the wood cut.
I hit the gun shows pretty regularly and have seem them as low as $75.00. This past January at the OC Crossroads show, I saw an SMLE Mk 5 barreled action for $200 dollars, and a Jungle Carbine barreled action for $100.
They're are out there, and they can be had for cheap, you just gotta hit the shows and gunshops. The internet auctions always seem way overpriced.
Good luck with the hunt!