I don't think you can go wrong with buying a dirt cheap 350D, especially if you are going to modify it for astrophotography where it has been the workhorse for some time now. Amplifier glow is not that bad and it may be easier to modify than the 450D because of the self-cleaning series of filters in the 450D. The live view feature of the 450D is an advantage of the 450D for astro work but the sensitivity of its smaller pixel imaging chip for long exposures is not yet known. There are also plenty of astro software and accessories for the 350D available now but these should come in time for the 450D. With the prices so low now for the 350D, I just might pick one up to astro modify as a spare.