Does your dispatch just use a mobile placed on the desk or are they going through the CAD for radio use? I know at least Motorola's Dispatch Radio software has a provision (might be a cost added plugin) for combining Nextel (sprint) Direct Connect into the system so that it's no different to the dispatcher than if you where to come up on a mutual aid channel; it's not exactly PTT easy but it can be several steps closer and we used it from time to time if batteries were dead or when we were still dealing with dead zone issues or guys would travel across the state it would be easier to go 41/42 for hours logging than holding up the tower on the other end of the state (which was against policy anyways) or trying to remember our number. Sometimes it's easier to get a little bit of programming added to an existing system than asking a personally owned radio be sent off for programming, also (and it pains me to say this but it's a fact of life) personally owned radios might be opening a can of worms if unions are involved and how exactly "on duty" is defined.
You can do an MTS2000 for a few hundred, but you'll need to get the radio shop guys to program it, if it's in house and you know the guys, not a problem; if your department takes them to an outside contractor prices start adding up, if you want to do the programing on your own of a Motorola it's a guaranteed headache (but possible). If you're not on a trunked system (PM me if you need help figuring that out) and it's just conventional stuff, then any radio made in the last 10 years that is legal to use on the public safety band (Part 90 type accepted) is narrow band capable that are pretty easy to get programmed, especially if you're only looking to have a handful of channels and don't need a fancy display (i.e. if it lives on channel one and just needs to be able to get you to ask for help), this could be done for sub $200 in some cases. If you start needing features to show your unit ID and the like you're back up to a few hundred. If you're on a trunked system this is probably going to end up as a no go.