If you are just looking for laptop style keyboards for your desktop then there are some out there. The ones I know are about the same price as Apple's though except for the MacAlly
IKEY5. I've never used this keyboard so I don't know how good it is.
I current own Kensington's SlimType keyboard which cost about $10 less than Apple's so it's not much of a savings. Like you I also prefer the feel of my PowerBook. The Kensington keyboard is nice but not as good to type on. I also got a chance to type on the MacBook's keyboard and I still think my PowerBook's keyboard is better. Apple's new slim keyboard is suppose to be similar to the MacBook's.
The problem I'm having with the MacBook's keyboard is that my fingers keep missing their placement because the keys are flat. There are no grooves for my fingers to slide into and I find that I'm a better touch typist with my PowerBook and Kensington keyboards. Of course this is all personal opinion so your results will vary.