I'm a stickler for optical quality and ruggedness and the least expensive I'd consider is a Weaver V3 1-3x20
. It's not illuminated but it uses good quality fully multi-coated Japanese glass yet you can get them for around $170. You could also look at a Nikon M-223 1-4x20
for around $300. I'm saving up for a Vortex Viper PST 1-4x24
illuminated tactical scope but those run $500 when you can find one. All of the above offer true 1x magnification at the low end for both eyes open CQB.
Weaver V3 on a S&W M&P15-22.