You dont see them in good shape very often, which keeps the value down. I agree yours are probably in the $50 range. Top loaders make more sense than slabbing.
Below is a 10-Poor slabbed for reference, an unslabbed, and a somewhat hard to find unslabbed blank back on thicker card stock.
F66 Barton, Larry (F+B cropped).jpg
F66 Grilk, Jim (F+B cropped).jpg
F66 Wasley, Mel (F+B).jpg