Digging through the UDXF archives (where more than a few of these DXers use SDRs), and looking for additions to our wiki, I found 3 which are under USD300! Not a bad way to get your feet wet, and the first one has some very positive reviews on eHam...
AFEDRI SDR-Net description
AFEDRI SDR-NET Product Reviews
Cross Country Wireless SDR-4+ general coverage receiver
Soft66LC Software Defined Radio
Soft66LC review on eHam
Needless to say the receiver links have all gone to the wiki, and I will dig the SDR related links out of the eHam reviews area in the next few days. I have also cleaned up a couple of the invalid software link references, so all the packages mentioned in the AFEDRI ad work properly.