I think I can offer some very good advice for you...
I'll list these in order of preference.
First, you can pick up some nice used Bridgeport Series I machines for less than $2500. It'll be difficult to convert one to a 3-axis CNC for less than $3000-$3500, but you might get lucky... However, this solution is hardly a 'benchtop' mill.
Your next best bet is to get a
dovetail Z-axis mill/drill like the one here: The Rong-Fu versions of these mills have a great reputation, but they can easily go above $3000 for a manual machine. Also, these machines are still quite heavy, most this size are over 600 pounds. You can pick them up from Enco, Grizzly, and many other places.
Slightly less desireable, but still very capable are the same sized machines with a round column Z-axis. They're just a pain in the butt to re-index the head every time you have to move it. I would highly recommend the dovetail Z-axis over the round version, even for the extra couple hundred dollars.
In both of these machines, you'll want to find those that have the highest spindle RPMs, as you'll probably be spending a lot of time machining aluminum and copper with small endmills.