As stated by 1gunsnotenough, they're generally pretty common.
There might be an exception for an unusual variation, such as a different drill/tap configuration. The vast majority of them came with three holes drilled/tapped. There were some early examples of the Competition Target that were drilled/tapped with only two holes.
One of them -might- command a premium, to someone specifically looking for that model. (I don't know if they were the same model number, or not.)
I'd guess that there are a few of the two-hole models out there owned by folks who don't even realize that they have something "different…"
There are a few recently completed GunBroker auctions. I didn't study them but it looks like $350-450 (+tax, +shipping, +FFL on your end) is pretty common.