IMO-YMMV
I have done an Extensive Amount of "Low Price" shopping this last 18mo.
I found HF rigs for under $300!
Most if not all were Not HRD compatible, or compatible in the sense that it made good sense to purchase some crazy interface to make it work in a ltd fashion.
If you could increase your budget about $150 you'd be on target (maybe just $100 but that may be a stretch). The Icom IC 718 can be found for $450+/-.
the IC 718 is Full Power, and works with HRD, past that ARFCOMM has proven it is a reliable low cost rig..
Try Craigslist, your Local Club and QTH Swap
Link
You will find a large selection of older Kenwoods in the $350-$450 range, the discussion rages on whether it's worth that for a 25+ y/o radio vs. a late vintage IC718....I have yet to come to a conclusion
again YMMV!