Let the hive mind of Engadget get that for you.
"I love my little computing companion but I often find myself missing a full sized keyboard. I have been looking at several of these portable and flexible keyboards, but I can't seem to make up my mind about which I should buy. I don't want the keyboard to be overly expensive, but I want it to be good quality. Also, how difficult is it to type on these keyboards? Thanks!"
Either way, I doubt it'll be too much of a difference.
I used to work in Dixons (an Electronics store) a few years ago here and we used to sell Tom Tom add-ons for those HP Mobile PC things...they worked out around £100-£150 with the adaptor, so they could be similarly priced I guess. I'm going to bet on £99.