I have several heated cat beds, both the flat kind and the cup shaped ones. They are very popular in my house. I like them because they only warm when a cat lies on them, and they don't get too hot, or use much electricity. You can probably buy the heating pad part and put it in your own cat bed. A good time to pick them up cheap is at the end of winter when the pet stores are clearancing them. I'd start checking the pet stores that sell them, like Petco and Petsmart, and watch for them to go on sale. That's how I picked up most of mine.
I should say I have picked up both the heating unit and the beds with heating units in them when winter stuff was being clearanced. And that can start as early as January, go figure.