Cheapest is dependant on what you own. Have a laptop already that runs XP, Vista or Windows 7?
Get Think Essentials and the bundled USB adapter together for much less than a stand alone programmer. Depending on your needs you may find that the Pro version is not needed. I've the less expensive edition (was 49.99 with the thinkstick but the price has come down).
Unlike the full functions of the Pro, my standard edition is able to do the following from the settings menu (besides linking and setting up a network of course).
Z-Wave Network
* join or recover another network
* Transfer primary role to another controller
Toos & Maintenance
* Backup or restore network settings
* Optimize and repair network
Events
* Change location
* View all events (where you also set them up).
Device Polling
* Change polling interval
Software and UPdates
* Check for software updates
* Upgrade to Professional Edition
ThinkStick
* Reset Thinkstick to factory defaults
Vizia RF+ Options
* Remote Sync (yep in case you purchase a stand alone programmer).