You can find one with the thermostat built in set at about 70 degrees. Buying a separate thermo will double the price, and for most gardeners an adjustable temperature is not required. Al

Many of us have used heating pads for sore back muscles. There was a time when one could get them quite inexpensively at thrift stores. There are Gardenweb threads here: heating mats and others can be found.

I think that the soil heating cables are just as effective, but cheaper than the heating mats for larger areas.

For several years I have used a heating cable attached to a sheet of plywood (to hold it in place - cable ties through holes in the plywood) covered with a vinyl sheet (to keep the wood dry). The plywood acts as an insulator as well.

Chad

I like the heating cable idea, Chad. Did you have to buy a thermostat with them?

I made a heating plate 3 feet by 6 feet using a 300 watt heating cable used for keeping rain gutters from freezing. I used a one half inch foam core which I covered with fiberglass enclosing the cable in the fiberglass. The foam acts as a heat insulator under the cable. A ten gauge aluminum plate was purchased from a metal salvage company and laid on top of the cable. An adjustable thermostat with a bulb type sensor was mounted on the plate. It has worked perfectly for over ten years. Al

My heating cable has a built in thermostat in the middle of the cable, I think that most of the budget ones are this way.

In my case I am not using it that way. I have the cable controlled by a separate thermostat set to turn ON when temps go below 45 degrees. I am using the cable to insure that a small section of my greenhouse is safe for overwintering starts of coleus etc.

The heating cable like chad describes is available from many locations. The longest one is about 180 watts and is good for about a four foot by four foot area with the builtin thermostat set for about 70 degrees. When I used this type cable I used 1/4 inch hardware cloth which I tied the cable to. If the cable is allowed to cross its self it will over heat at that point and burn out. I first tried covering the cable with damp sand and setting my pots on it. This only worked as long as the sand remained damp,not long. Then I used about a 20 gauge aluminum sheet directly on the hardware cloth and cable. This worked well for several years until I needed more room. I left it plugged in 24/7 as it only heated when the temperature dropped below 70 degrees. Al

By hardware cloth, do you mean window screening and its more modern substitutes?

Rain2Fall

Have you considered shopping at thrift stores or yard sales for a waterbed heater?