so whats a good (relatively)inexpensive radio that can operate on fast food frequencies out of the box
I've looked into it a bit and so far it looks like the Yaesu VX-7R is about the cheapest you can buy for this kind of thing. I guess you need a tri-band because the fast food places broadcast in a few different ranges, so you don't know what you'll need exactly in terms of frequencies.
The radio manufacturers have to block certain frequencies to comply with FCC standards, so you can't actually buy one that works out of the box. You'll have no choice really, you'll have to mod, but from what I read it's a very simple modification. Just about anybody could do it.