The post office should have a scale you can use yourself. Just use it to get the # of ounces and they should have a chart that lists the price for each level. I haven't waited in line for a long time, except to mail out my tax returns with the confirmation. I >could< do the confirmation thing myself, but it's a little more complicated and I don't do it often enough to remember how to do it.
BTW, I think I sent out 2-3 CD's once, wrapped in a cardboard thing, and it was 2 stamps. I usually put an extra stamp on it, just to be on the safe side.