Any amp with a 1/4" input will allow you to plug any of those instruments into it... Generally, the differences between bass amps, acoustic amps, and electric guitar amps are just the prupose they're designed for. That doesn't mean that they can't be used for other instruments, it just means they're not optimized for that use.

Check out any of the Line 6 practice amps... pretty inexpensive. They will cover your electric guitar and acoustic gutiar pretty well but the bass response will be low when you plug in your bass...

You will probably have to adjust your levels when going from one to the other in order to compensate for the differences in outputs... not a big deal though.