OP, congrats on the ambulance. I'm pretty sure I saw some of your guys at the NCEMSF conference.
I sympathize with the need for conserving funds, but you need to know what you need before you start asking for stuff.
Some thoughts:
If you're putting a state-licensed ambulance in service, you may actually NEED to have County or Region radio communications in the vehicle. If you're a BLS agency, what happens when you need an ALS intercept? How do you communicate with them? At my service (Campus based first response) we have 2 separate radio systems - one for local use with the school PD dispatcher, and another one for use with the County dispatcher and other units. It can be a little annoying, but it's very nice having both links at different times.
As for the local school radio system - there are a number of different bands that Emergency Services radio system commonly operate on. Very few radios will work on multiple bands (and the ones that do cost a LOT more).
Another thing - Narrowbanding is coming, if it isn't there already. That means you need a new(er) radio that is capable of narrowbanding, otherwise you'll run afoul of the FCC.