What do you want to listen to ?
Desktop or Handheld ?
My favorite by far is the GRE PSR-400 it will pick up about everything but digital and for about 180 dollars with shipping it leaves money left over for a external antenna.
Answering this question and staying within your limits must come with some cautions. Many agencies out there are moving to 'digital' transmissions. If you want to monitor one of them, you'll need a digital scanner. It is also worth noting that there are some agencies which can not be monitored by ANY scanner.
To keep within your budget, I suggest the PSR-300 hand-held scanner. I bought mine from ScannerMaster (see link at top of page) for $149 which included shipping and the AC adapter. But the scanner is probably not the only thing you are going to need to purchase. Other items include: a programming cable, programming software, rechargeable batteries, possible alternate antennas, external battery charger.
Certainly if you are going to use the unit at home, or in a vehicle, and NEVER portable; then the PSR-400 base model is good (it is the base version of the PSR-300). But as soon as you want to carry it with you or run it from batteries such as during a power outage, you'll want the '300. I have an outdoor antenna at home and a magnetic mount antenna on my truck.
If you want to monitor an agency which is digital, then I suggest the PSR-500. Unfortunately just the scanner will cost more than $400 unless you wait for a sale.
The PSR-300/PSR-400 are organized as 10 banks of 100 channels each for a total of 1000 channels. This is a lot easier to learn how to program and operate, but often "wastes" memory. The PSR-500 (or PSR-600 base model) use "object oriented programming" and are much more difficult to learn, but can be more flexible to use with the myriad of complex systems out there we want to monitor.
And we know nothing about where you are located so we can see if a $300 scanner will get what you want.
Welcome to RR. It would help greatly if you would go into your User CP (found in the blue toolbar under the thread title) then click on Edit Your Details in the left frame. Put in your county/state. This will help narrow down your responses to those folks that are in your general neck of the woods