Well the 2100 pts are actually only £15 at most places, I say most places, I only know that it's that price at Play.com and Amazon.co.uk... but I would assume others are around that cost. Dunno if that helps, as your still be getting the game for £25. Although in that respect the 2100 pts are £3 more. Overall saving £12 if bought separately.
I was in a dilemma the other day, as I got a £15 off voucher for Amazon, so could get the game for basically £25 (excluding delivery), but was then curious about delivery timing.
I also completed Rage last night and was curious on what to do with it. I have it pre-ordered at Game, and found out I could get £25 trade in, better than cash at CEX so took that then and there haha, with Dead Space 2 (only £4 but couldn't be bothered to go elsewhere).
I bought Rage for £25 to begin with, well chuffed with that, so got fiver pre-order, £29 trade in and it's a midnight launch.
I am not sure on the cost in store though, hoping it's £40, but Batman and Fifa etc have been something stupid like £42. So I am looking to now spend only about £6-8 depending on in store price

Happy days, and that Amazon voucher can go towards Uncharted 3 or Modern Warfare haha.