To add to this, there are many variables that need to be considered. Properly frequency separation, licensing, RFI avoidance...etc. If your area has a public safety trunking system and your a legit entity, they should be willing to give your group a talkgroup on the system.
Avoid in-band operations at all costs. If your agency uses VHF, then use a UHF VRS style repeater. If your agency uses UHF, then use a VHF VRS repeaters...etc.