Monoprice also has house brand RCA plugs for $1.80 each. They don't look awesome but I've used them in projects and they work perfectly OK.
Monoprice and Markertek have better prices than Redco, but only if you're ordering a large quantity of stuff since you're looking at a base shipping charge of $5-8 on top of your order, depending on where you live.
For ones-and-twos things like this, Redco is probably your better bet. They also have the Neutrik NYS352G for even less than the house brand plug; I haven't tried this particular connector but in general Neutrik's NYS series have been good to me.
10AWG wire might technically fit through the opening in the plug shell but you'll have a hard time soldering it to the plug's tabs. Not to mention trying to get the plug shell over the joints once you're done, since the wires won't be laying flat around the joints.
A quartet of ultra-short 10AWG wire (what you need for a stereo connection) can be stiff enough to lift your equipment right off the shelf, too.
If your goal is to build a very short interconnect you gain little or nothing performance-wise from using massive cable; electrical effects are cumulative over distance and your cable run is considerably shorter than average. Inside your equipment, electricity is going to be conducted over much longer distances through much smaller conductors, and you don't seem to mind that.
Try building something with 24-22 AWG or so for your first project. No larger than 20 AWG. This will still be large for your purpose but not unwieldy. You'll be plenty happy with the result, I think.
Edited by ardgedee - 11/27/12 at 4:42am