I know I can get one made but I put my STC together and fancy trying this as well.
http://www.ebay.ie/itm/Digital-PID-F-C-SSR-Thermostat-Temperature-Controller-PT100-Thermocouple-TE075-/161450916519?pt=LH_DefaultDomain_3&hash=item2597397aa7
Would that be ok with a probe from brew builder all...