What's an original Cherry thick dyesub set in good condition worth? 
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Also a GMK purple set?
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Thanks!
Dyesubs run the gamut, I'll let Photekq get that one.
As for GMK purple, the new full set went for $41 + shipping.  Yours is missing the following keys:
- Full-touch Caps Lock
 - 2.25x Shift
 - Both 1.25x Alt
 - Both 1.25x Ctrl
 - Three 1.25x blanks
 
It also has two additional 1x Ctrl keys.
It's unusable with standard keyboards and only (mostly) works with winkeyless G80 or Korean keyboards.  Even then you're missing a shift.
Since it's such an incomplete set and missing 7 keys that came with the original (9 if you don't count the extras that replaced them, which is just under 1/3 of the original set of 32), I'd say $20-30.  It's definitely not worth the full group buy price.