When I've set up P25 receivers, it's common to use 2-4 RTL-SDR's to do the bulk of listening. Each rtl-sdr gets set with a different center freq, and the control channel tells when and where to listen.
You'll use https://www.radioreference.com and get the appropriate control and voice channels for your area. You'll also get the talkgroups and put them in a CSV.
From there, you'll use http://garvas.org/trunk-recorder/ to determine how many RTL-SDR dongles (or others) you'll need, along with their respective center frequencies. Note that you'll copy/paste the relevant control/voice line for your p25 from radioreferece.com
You can build a P25 listener for less than $100.