As I mentioned on the Softrock forum, I'm working on a small system like the Xylo, but using the newer, bigger and better Cyclone II EP2C5T144 FPGA. The forthcoming KNJN Saxo board probably uses it. My board will just have the parts for an SDR on it, PIC18F2455 for FPGA configuration download and PC comms, the FPGA and a suitable ADC (probably the Wolfson one), and will be very cheap.
I've been told that the '2455 doesn't work properly for full-speed USB 2.0, but can't seem to pin this down. I've just designed a small home-made PCB with just the '2455 on it that I can try out, before I commit to using it with the FPGA.
I've got some EP2C5T144 chips on order from Altera (about $12 each plus shipping etc.), and should get them next week. I've created the EP2C5 part for the Pulsonix PCB software I use, but need to finish off defining the pin net names, which will minimise the chance of design errors. Altera has a useful spreadsheet for the pinouts, which saved me a lot of time as I could just copy/paste the pin logic names into the Pulsonix part editor.