Most Canons from the 450D up have Liveview and Back Yard EOS ( BYE) software is cheap ( cheaper than an intervalometer ) and would manage an imaging session much better with lots of added features.
1100D was touted a while back as being the bees knees. Been overtaken now but it's quite cheap I'd guess and still a good starting point. One listed on here a week or two ago for only $250 I think for the body.
I bought a $70 450D body with supposedly a problem ( easily fixed ) as a starter, quite happy playing with it. You don''t have to buy new and you can dedicate a cheap camera solely for astro raher than trying to justify it for normal and astro purposes.
BYE is awesome btw
T-Ring is needed for prime focus, you need that to be serious.
EQ5 would be the minimum mount IMHO, EQ6 much better. But that might blow your budget. In Astrophotography the mount is everything.