Hi Chris,
Wilson's Fine Violins is in Birmingham, MI about 10 mile north of Detroit. It's definitely a high end string shop, but they do carry some student instruments. I get the impression that they can do just about any kind of setup or repair, and seem to have a lot of collective bass knowledge and experience. Their number is (248) 258-0370
Elderly Instruments is in Lansing. They're more of a guitar oriented shop, but do carry quite a few acoustic instruments, including a lot of violins and a few basses. I think their repair department is also more guitar oriented, so I can't really say how good they'd be for bass setups and repairs. They'd probably have a bigger selection of pickups than Wilson's and they're usually pretty good about letting you try things out. The place can be a zoo on Saturdays though. I don't have their phone number but they're on the web at :
http://www.elderly.com
HTH,
Ric