Yep, 1/144th is the scale. I own both kits, the original with the Enterprise, and the later one with the Challenger, which includes decals for other shuttles, but don't know if it has the aerodynamic shroud that the Enterprise does.
Off hand, I don't recall what I paid for the Challenger model (bought it last summer on eBay). I know that I paid about thirty dollars for the Enterprise, but that was ten years ago at the LHS.
Don't know what search MadModel did, but a quick search on eBay just now turned up three. One Enterprise, and two Challengers. Here's the link:
http://search.ebay.com/search/search.dll?query=1%2F144+747&catref=C3&socolumnlayout=3&from=R2&sacategory=1188&sotextsearched=2&BasicSearch=
I'm not trying to talk you into justifying the price, but consider that you are getting two models in one, and rather large ones at that.
stinger