I have the USB Winkeyer -- it's the "Cadillac" solution to the problem. And it's not hard to put together, if you can solder. No surface-mount soldering is required.
You can get a USB-to-serial adapter, and a kit from W3YY:http://www.w3yy.com/fsk.htm
If you're using Windows 7 (or 8, I suspect), get an adapter based on the FTDI chip, not a Prolific chip. Check eBay for sources.
Now, somebody will supply a source for the single-transistor circuit that substitutes for the W3YY kit . . .