Butchering a laptop might be the most economic idea (ironically), you can pick them up cheap on eBay... Cheaper with a broken screen (which you won't need)... Keyrah looks like it will do the job... Though I have no experience with one.
I too have to agree, I never done a full mod so I was put off it, but I did see just about a month ago at a computer market an Acer Aspire One with a broken screen for just £40 and it did cross my mind, get it and rip out the motherboard to make my own all in one keyboard, but like I say I've not really done mods and as I'm saving up for a possible very dear computer (x1000 or sam460) I decided ageist it.