Tool type
Specialty planes do one job a bench plane can't. Stanley's No. 45 and No. 55 combination planes plow, rabbet, bead and mold with interchangeable cutters. The No. 71 router levels the bottoms of dadoes and recesses, the No. 78 cuts rabbets with a fence and depth stop, and the nickel-plated No. 92 trims tenon shoulders. These are the planes most often sold incomplete. Fences, depth stops, cutters, collars and thumbscrews all come off, so count the parts in the photos against what the plane should have. Patrick Leach's Blood & Gore is the reference for what each one shipped with and how the features changed.
5 models we cover.

Stanley · Specialty plane
No. 451884–1962
$90–$260 typical ask
84 on eBay
Stanley · Specialty plane
No. 551897–1962
$500–$850 typical ask
31 on eBay
Stanley · Specialty plane
No. 711885–1973
$100–$230 typical ask
101 on eBay
Stanley · Specialty plane
No. 781885–1973
$40–$65 typical ask
116 on eBay
Stanley · Specialty plane
No. 921902–1969
$130–$170 typical ask
10 on eBay