You were probably thinking the prices were too high
List of cardbacks (from memory mostly):
25th Anniversary April O' Neil
25th Anniversary Michelangelo
1988 April O' Neil (LATER VERSION with orange stripes on suit and larger hair)
1988 Bebop (later variant with many figures and weapons featured on back)
1988 Donatello TEN BACK
1988 Foot Soldier TEN BACK
1988 Foot Soldier TEN BACK
1988 Michelangelo (later variant with many figures and weapons featured on back)
1988 Splinter TEN BACK
1988 Splinter TEN BACK
1998 Donatello
1994 April
1994 Bebop
1994 Foot Soldier
1994 Shell Kickin' Raph
1994 Storage Shell Don
1994 Storage Shell Leo
1994 Storage Shell Mike
1994 Splinter
Dirtbag
Fugitoid
Grand Slammin' Raph
Groundchuck
Hose 'em Down Don
Mike, the Sewer Surfer
Mondo Gecko
Napoleon Bonafrog
Panda Khan
Panda Khan
Rahzar
Robotic Bebop [1998]
Slap Shot Leo
Slash
Space Usagi
Storage Shell Don
Storage Shell Leo
Storage Shell Raph
Super Shredder
Tokka
Triceraton
Wyrm
Bandito Bashin' Mike
Chief Leo
Sewer Scout Raph
Movie III April
Movie III Princess Mitsu
Movie III Princess Mitsu
Movie III Samurai Don
Movie III Samurai Mike (card badly bent)
Movie III Walker
Movie III Warlord
Next Mutation Donatello
Next Mutation Leonardo
Next Mutation Vam Mi
Next Mutation Michelangelo Thunder Thrasher
Pizza Tossin' Leo
Pizza Tossin' Raph
Pro Pilot Don
Shogun Leo
SuperMutant Mike
Toon Burne
Toon Irma
Toon Kala
Tournament Fighters Rocksteady (card badly bent)
UnderCover Michelangelo