A question from a total beginner

My nine-year-old brother's birthday is coming up, and he desperately wants a telescope, so I've been trying to find one in the $100-$300 range (who knows, maybe I can get an even better one used off Craigslist). As I researched this, it occurred to me how cool it would be to hook up my camera to whatever telescope we buy and grab some shots as we stargaze.  If I remember right, you can use some sort of adapter (a T ring, maybe?) to hook up an SLR to telescopes.  I have a 5D Mark III, which I imagine could be good for astrophotography because of the clean high ISOs.

Can you hook just any telescope up to an SLR, or only certain kinds?  If only certain kinds, are there any in the $100-$300 range that have this capability?

Any guidance you can give would be appreciated!