The original GP100 327 in as new condition will bring around $1000. I would not sell mine for that, but some folks would not pay that either. I have seen them sell for as high as $1250 and as low as $500. Depends on how bad some one wants one I guess.
Ruger just released a blued GP in 327 a few weeks ago so prices on the original run may be reigned in some what. The Blackhawks are bringing premium prices also. Ruger has not rereleased the Blackhawks yet.
http://www.lipseys.com/itemdetail.aspx?itemno=RUGP32751