Not sure where the idea that you have to wait between images with a DSLR comes from ? I have taken 100's of images with a DSLR and have never ever done this. Out of habit I program a 15 - 20 second pause between images but this is to allow download of frames to the Flash Card not for cooling.
You can pick up used 300D's now for less than $1100AU and pulling the filter out of them is pretty easy with step by step, screw by screw instructions here:
http://ghonis2.ho8.com/rebelmod.html
I agree that the ability to do Ha imaging with a monochrome CCD is a real benefit of a monochrome CCD.
Regards
Chris Venter