Here's my homegrown heated bed. I decided to make my own because prusa's needed a bigger board than I had available.
Resistance measures at 0.9 ohms although my multimeter isn't exactly accurate with stuff like that. Eagle's length-freq-ri ULP also pegs resistance at about 0.9 ohms.
It reaches about 116°C with ambient of 10°C, a felt underlay, and my power supply's 12v rail drooping to about 11.3v despite two 12v 50w lights loading the 5v line.
Here's the eagle BRD file for those interested: Heated Print Bed.brd.
Just need to add a proper surface now, and see how it goes!