Instead of asking how configuration affects the price which leads to an almost unlimited discourse, the best thing to do is to let one know the exact configuration, pictures are a must at the minimum for even a ball park estimate as refinishing varies considerably and whether or not the gun is in its original configuration. SKEET M21's have specific attributes if a gun from stock and not a custom order. There is also the difference between SKEET grade and a M21 SKEET which is a little more subtle in that a SKEET grade was a pricier version while the first SKEET model had 26" barrels as standard.
Actual choke measurements, chamber measurements and possible barrel wall measurements should be made. Stock dim's would also have a lot to do with whether just purchased and coveted or actually used. SKEET M21's were also used and advertized by Winchester as the perfect upland gun as well as target guns.
BTFE, ejecters, SST and checkered butt, are all attributes of a SKEET M21 which could be had with either pistol or straight grip.
So, in short, your gun could vary from say 4-5K to possibly 8K but it all depends on much more information and pictures plus in the final analysis, actual evaluation. Initially sounds like a nice 20 gauge M21 in a desirable configuration.-Dick
Last edited by Dick_dup1; 09/27/08 05:18 AM.