Rams123 -
Buddrousa is right. For your area, you need P25 phase 1 digital trunktracking and DMR capability. You are not going to find that anywhere near $100, even used. You might be able to find a used Uniden BCD436HP or BCD536HP for around $425 - $450, but you will need to fork out another $50 for the DMR upgrade. I'm not sure about the used price for the Whistlers (I'm a Uniden guy), but I'm guessing they're in the same neighborhood as their similar used Uniden counterparts.
The technology is evolving and the radios are also evolving to support the newest digital modes, but they are still very pricey. IMHO, the prices on radios that support Phase I and II plus other digital, such as EDACS and DMR will NEVER be inexpensive (the price level you stated you want to spend).
You're either going to need to wait a considerable amount of time before they come down in price in the used market (by "considerable", I mean in years), or change your budget now.
There are other options you can cobble together now that will cost less, but still not $100.
For hardware, there are several options. For example, the RSP (Radio Spectrum Processor) from SDRPlay, $150 new, or the AirSpy SDR Receiver (R2), $199 new. Just FYI, in case you think you might be interested in HF receiving in the future, the AirSpy only goes down to 24MHz, so you would also need an upconverter, such as the 1KHz - 60MHz SpyVerter, $49 new, or the DC - 55MHz Upconverter from SV1AFN, $57 + $12 shipping to USA. BTW, I use the SV1AFN with my AirSpy and other radios and it works extremely well. I've bought and assembled several kits from Makis SV1AFN, as well as buying pre-built products from him. Everything he produces is exceptional quality (and it is priced appropriately), i.e. you'll pay a bit more for his upconverter than other, cheaper models, but IMHO it's well worth it. I'm NOT saying that the SpyVerter is not a good product; from everything I've read it works very well. I use the SV1AFN upconverter because I already had it for use with other radios. The SDRPlay goes down to 10KHz natively, so no additional hardware is necessary to get HF coverage. If you do decide to buy an upconverter for any radio, either now or in the future, do your homework before buying. Upconverters vary widely in performance. In general, you get what you pay for when it comes to upconverters.
I listed just the two SDR radios (AirSpy and RSP) because they are inexpensive and perform reasonably well. You can buy a $10 SDR, but as with many other things in life, here you also get what you pay for. The AirSpy and RSP are 12-bit processors. The el-cheapo SDRs are 8-bit. This DOES make a big difference in performance. Google is your friend when it comes to comparing the very inexpensive SDRs ($10) to the mid-low end SDRs ($150-$200) to the mid-high end and high end SDRs ($250+). Another one to consider is the Afedri SDR. It's also a 12-bit SDR, but is in the $250+ range. The big difference between the Afedri and the other radios is that the Afedri has both USB AND Ethernet interfaces. This makes it very easy to network the Afedri from anywhere in the world with no additional hardware or software required. The Afedri has numerous options, such as a dual channel model. Look it up to get more information.
Once you have a SDR, you need software for scanning and digital decoding. Digital Speech Decoder Plus (DSD+) software decodes numerous digital modes, including what you need for your area (Phase I + DMR). Unless you want to tune your SDR manually, you'll also want a package called "Frequency Manager Suite" from Jeff Knapp. This is a FANTASTIC piece of free software that turns an SDR into a scanner. It works with SDR# (AirSpy), SDR-Console (AirSpy, RSP, Afedri) and SDRUno (RSP).
So, in summary, for somewhere between $150 and $200, you can buy a SDR and get the free software needed to turn your SDR into a scanner that decodes various digital modes. NOTE: this combination will NOT do trunk tracking. That's the huge difference between the cobbled together solution and paying $500 for a radio that does it all, including trunk tracking.
In short (I know...too late), find a way to increase your budget and get the best solution now. Yes, you can nickle and dime yourself up to a trunk tracker. However, in the long run, you'll pay more than if you just buy it now.
I hope this helps.
Best regards - David S.