HI, I just thought I would give you my views.
I live on my own and have my bathroom heated by electric underfloor heating (devimat)
The bathroom measures 2.5metres by 3, so quite small.
Had the floor fitted Nov 2007, first bill for nov 2007 to-jan 2008 was £113
Second bill Jan 08 to April ahd just come in at £130. Electricity bills for me are usually about £50-60 per quarter so I would say yes underfloor heating costs!!!
I had the floor coming on at 5-30am to 9am and eve from 5-30 to 11pm on about 30degrees. Have now considerably turned down the length for which it is on, and the temp.