This year I waited too long before buying a seed mat from Smith and Hawken's liquidation...but after I came across
Jimche's post here on TV and doing some research online, I decided to try rope light. I'm too lazy to build anything and being in So Cal there is plenty of sun, so I threw together a mini hoophouse and ran power off a GFCI outlet to a timer leading to the rope light and a fan. Oh, again I didn't set anything up like the link above just set a 10x20 flat atop about 6 feet of rope light. I can take pics but there is nothing really spectacular about it.
I am happy to report it works great!
The soil temp indoors is around 75 degrees but since it was outdoors the temp hit 95! I hope I didn't kill them.
I hope this helps anyone who can't invest in an expensive heat mat. I'm sure there are ways of raising or lowering the plants above the lights, putting a material between the the two, or using a dimmer to regulate the output of the lights to get the right temp. Anyone else using rope lights?