How do you guys value rare moder variations?

[richtree]

Here are some rare ones I picked up over the years and people have asked me to buy some but I never know what is the correct range when they are just so rare.

Here are some below in pictures:

1980 topps Greg Pryor missing name
1980 topps Jack Clark no position
1989 Fleer checklists with positions
1986 Terry Puhl Blue Streak
1991 Topps doug Drabek White border
1986 Sportflics Robin Yount YANKEES version

I have many more but for example the Yount I have seen sell from 100-800, so I am assuming that is "the range" but don't want to give these away either...