Haven't played the demo, but I was a fan of the original TM, and Sunrise is a brilliant sequel. The lack of collision will put a lot of people off, but for time trial style gameplay and track designing, it's the best racer there is. The game will tell you when you acheive certain stunts, but stunts do not have any purpose in terms of points - however, the Trackmania community is sure to have a few stunt teams around, and there are stunt video competitions around too. The cage thing appears to be some sort of loop, although the game has many tiles which are used for multiple purposes - one of the things that means new tracks can still amaze after playing the game for a long time, and aids the discovery of shortcuts for the sneakier racers
It might not be the same everywhere, or it might have changed, but TM:Sunrise was only £15 in woolworths when I bought it, less than a month after release. Certainly worth getting, although you should also get an analog joypad if you don't already have one, since accurate control often determines the outcome of a race.
Megaton - it's the sequel to a game that came out a couple of years ago and received a sort of cult following, particularly amongst fans of the Micro Machines games, and the ST/Amiga classic Stunt Car Racer. It's not a DB game.
