PC9 sorta screams red dot to me, but to each his own. I would put Crimson Trace CTS-1400 on it.
If you want a light weight scope, SWFA SS Ultralight 2.5-10x32 at less than 10 ounces should be on your list.
Unfortunately Weaver discontinued their V3 1-3x20, but it would be a really good option.
Leupold VX-Freedom 1.5-4x20 is also pretty light weight.
ILya