Go Ducks!
Man, that was a long time ago! I was just thinking about my old
girlfriend dorm room yesterday. Yup,
Disco was in to give you an idea.
Anyway, you mention 2 very different things (sort of). You
can get a 70-300
with a macro, but I really wouldn't recommend it (Sigma 70-300 macro). It's cheap alright. Very inexpensive. Did I say cheap? I have a bunch of terribly soft shots if you'd like to see any.
Here's a multi-lens shootout I did with it and others on a single subject.
http://forums.dpreview.com/forums/read.asp?forum=1043&message=42131858
Anyway, a good lens to try for (although I've had terrible luck) is the Tamron 70-300 VC. It's what prompted the shootout.
IF you get a good copy you'll have a lot of technology and a very nice lens with amazing vibration compensation. BUT it's not a macro. I have some more very sharp and wonderful samples from this lens if you're interested. You can read at that thread more than you'll care to know about all of my thoughts on it. It's $450 and there's a $100 MIR through October right now.
But
back to macro.
Bang for the buck macro? Look to the Sigma 50 f2.8 macro. $370. Great lens.
http://www.photozone.de/canon-eos/299-sigma-af-50mm-f28-ex-macro-dg-test-report--review
Of course for a bit more there's the Tamron 60 macro and the Sigma 70 macro. And for even a bit more, you simply cannot go wrong with the EF 100 f2.8 macro (non-L). It will last a lifetime. But, we're starting to gett away from "bang for the buck" here.
For a general lens-lens, it's hard to beat the EF-S 18-55 IS, or the nifty fifty. These are both better than they have any right to be.
Another excellent third party solution is the Sigma 17-70 f2.8-4 macro OS. It's about $470, but really is a do-it-all walk around solution.
Don't forget to check the Canon shop for refurbs, they're shipping free right now I believe.