I put a single Cessna 185 seat in my old C170 via field approval.
Not as handy as a folder, but since the backrest slid right out and the bottom was so easy to remove / reinstall,
it was pretty close.
Mounts pretty far forward, as noted by others, so not as much legroom as a BAS or Dodge folding seat.
I have BAS folding seats in my current 180.
I've always liked them a little better than the Dodge seats,
more comfy seating for one thing unless you add padding.
But the Dodge seats may be a bit more versatile, with a little fore-and-aft adjustment available,
plus the Brownline type rails they use on the floor and sidewall also fit readily available cargo rings.
The old BAS seats are now made & sold by Lakevue Aero,
a single seat costs $1300 and a pair costs $2300--
not including seat belt mounting parts. That's another $250 for two seats worth (not including belts).
http://lakevueaeronautics.com/id2.htmlAtlee Dodge also sells single seats, $1500, or $2950 for two.
This appears to include seatbelt mounting hardware (but no belts).
http://www.fadodge.com/removable-folding-jump-seats/