Best winter heat for orchids?

[Orchidreamer]

During winter, the temps drops down to 65 degrees. I don't want to turn on the heat and heat up the whole house due to high utility bills. This year, I have several warm-growing phal species seedlings that require warm temps, so I'm considering buying a heating mat or any kind of heating apparatus for heating about 10 seedlings in 3" pots.

I want a good quality, reliable heating mat/apparatus that's safe to use for long periods of time. I'll be using it nonstop for a couple of months. Any recommendations?

Note: I do have a portable heater that can heat up the whole room, but it's too "extreme" -- it's basically baking the air!