When I bought this it was $17: the digital heat sensors https://www.amazon.com/VIVOSUN-Digital-Seedling-Thermostat-Controller/dp/B015F4VFGI/ref=pd_bxgy_86_2?_encoding=UTF8&pd_rd_i=B015F4VFGI&pd_rd_r=1HCKJXJJBBV0NW2W1AYK&pd_rd_w=fJNYN&pd_rd_wg=iKA5l&psc=1&refRID=1HCKJXJJBBV0NW2W1AYK

Here is the heat pad, it is always on full blast (you put it under the tray and the heat goes up, and put the heat sensor at the top so when the thing is fully heated, it turns off) : https://www.amazon.com/Plant-Babies-Heating-Waterproof-Seedling/dp/B013HFKRMK/ref=pd_sim_86_3?_encoding=UTF8&pd_rd_i=B013HFKRMK&pd_rd_r=1HCKJXJJBBV0NW2W1AYK&pd_rd_w=152tJ&pd_rd_wg=iKA5l&psc=1&refRID=1HCKJXJJBBV0NW2W1AYK

Or you can use this programmable controller the head: https://www.amazon.com/bayite-Fahrenheit-Digital-Temperature-Controller/dp/B011VGASLW/ref=sr_1_5?s=hi&ie=UTF8&qid=1481436370&sr=1-5&keywords=digital+heat+switch But you have to do some wiring (outlet cord, and wire an outlet) and you have to read up on how to program it

I use the programmable timer for Quail and the timer above in the first link for grow trays/starts. Either combination should work. Can you post pictures of your worm farm? Thanks