John,

I got X-10 stuff from the following 2 sites:
http://www.x10.com
http://www.smarthome.com

Just a couple of shopping tips:
1. Registered your email at both sites.
2. x10.com will send you special deals (which happens everyday, so don't buy their "last day!" gimmick).
3. Wait for "Free Shipping" at smarthome.com. It happens from time to time.
4. The IR-to-RF you're looking for to be able to control using the Pronto is a product named 4040. Search for it at the smarthome.com site. It is made by X10 but they only sell it through smarthome.com

Good Luck and have fun...