I think Flex radio is probably the only plug and play computer based HF transceiver out there and you can get started for under $500 used. I have a Flex-1500, which is a 5w QRP rig that covers 160 through 6m and it has a world class receiver and sounds excellent on transmit. There are other ways to do an SDR transceiver but that usually involves running Linux and cobbling together amplifiers and filters to get any useable power on transmit.
prcguy