Starting at $2500 sounds smart. The later bikes don't pull quite the stupid money that the early models sell for, but it's still a CB750. My rule of thumb for a bare minimum rider is $1000. This is either a basket case for (say) $500 that needs $500 worth of work to get going, or a rough-looking but mechanically "acceptable" bike for the full $1000. This is worth more than that.
Plus, unless you're dead set on getting your exact asking price, you'll want a little negotiating room. List for $2.5K, you may negotiate down to $2K and still feel good about things. If you don't need it gone right away you might even start higher, maybe $3000, just to see if anybody bites.
Ultimately, "value" is whatever you can get somebody to pay for it. Good luck.
