If they want to charge for a demo, they should charge just enough to cover distribution costs. I mean, I wouldn't mind paying $1 for a DVD with a demo on it. Any more than that and they are essentially getting you to foot the bill for the advertisement.
Although, I agree with Deneidez, there are enough people who would probably be willing to buy this crap. Just look at the playstation blog suggestion area where every single suggestion has "i'd be willing to pay, just implement it." Not only that, but people buy/preorder games to get into beta's or play demos. The videogame industry seems to be filled with tons of raging gamers who love to waste their money and have their hands on things NOW.