Do industrial-bus SBC's, like STD bus, count? (These are definitely not consumer stuff.) The one I used in the ATE shown at
http://www.6502.org/users/garth/projects.php?project=6 was a Cµbit 7540. It cost $295, ran at 2MHz, and had a 6522, 6520, 6551, 6532, and seven 8KB memory sockets, most of which could be either RAM or ROM. There was also a 7530, 7520, and 7510. Cubit was a division of Proteus Industries.
Two others in the STD Bus Buyers' Guide at the time (1990) that were 6502-based were:
Enterprise Systems Corp. 10812 at $260
HiTech Equipment Corp STD-65F11-00 at $199
These, being STD bus, could be put in a card cage with other cards for added memory, disc-drive controllers, video controllers, serial & parallel I/O expansion, IEEE-488, analog I/O, communications controllers, etc.; but the individual SBC of about 4.5x6.5" was a complete single-board computer. For the ATE, I used a couple of off-the shelf STD-bus signal generators and an A/D board, and made the rest: programmable power supplies, loads, relay boards, DVM board, and others.
BTW, "STD" came from "simple to design," not from "standard."