If your budget is only $400, you will have to find something used. A new digital scanner will run $500+.
I would also highly recommend the Uniden BCD396T, mainly based on my personal experience with mine. I think the 396 is a much better scanner for ARMER because of Uniden's dynamic memory.
Take a look on ebay, there are usually quite a few digital scanners for sale. I picked up my 396 on ebay 3 years ago for $400.
You could also check Craigslist, there are sometimes a few people on there with scanners for sale. I just looked and there was someone selling a Pro-96 for $275.
It also wouldn't hurt to check some pawn shops, they get a few scanners once in a while. A while back I found a Pro-96 at a pawn shop for $200. I couldn't pass that deal up so I bought it but I decided I didn't like it. I put it on ebay and it sold for $300.
Also, if you aren't ready to spend the money on a digital scanner, there is still stuff you can hear with your old scanner. See this thread:
VHF Freqs?