Chris L Peterson wrote:

The one and only useful feature the 10D has that the 300D does
not (for astroimaging) is shutter lockup. I have no idea
what "limited functions" means to S&T.

For "normal" camera use, there are big differences between the 10D and
the 300D:

http://www.photo.net/equipment/canon/10dvs300d.html

For astrophoto purposes, though, you are right: the mirror lockup is
the #1 change. And one that can be effectively simulated by removing
a cover, so its not that big a difference in the end.

You can now get a 300D body for under $600. That's tough to beat!

Modified 300D for astro-photography:

http://www.sciencecenter.net/hutech/canon/index.htm

The bad news:

http://www.sciencecenter.net/hutech/camlist.htm

.... $1500.