Today, almost all AR's are pretty close in basic quality. For a basic shooter there is little difference. Olympic Arms did go through a growing/leaning stage. Today, they make good weapons. In fact, they are one of the few that makes their own barrels, receivers and major parts. Their ultra match barrels are pretty good.
Unfortunately, you are a little late. From around the end of October, every AR manufacturer sold every major part for AR building. Then the Shot Show was last week and now they are all back orders beyond June. I'd not be in a hurry. The pricing on lowers is through the roof on Gunbroker with tons of gouging and panic buying going on.
I had twelve AR's in stock at the time of the election and they all sold in 4 days. I've just about gone through my inventory of parts and have had my re-stock orders in on backorder for 6 months. (I'm a DPMS, Rock River, Stag, Oly Arms, Yankee Hill, Daniel Defense & Bushmaster dealer).
With CNC quality machining, I haven't seen a sloppy lower or upper receiver in two or more years. The Mil Spec on the finish is standard and all are quite good. The big names usually seals the finish with a Teflon black. Very nice, but not necessary for good function.
Take your time, you should be able to find a good lower for under 180 in a name brand. 150 for a non-name. When pricing stabilizes, 110 to 120 for an average good lower. Check Del-Ton for parts, M&A sells kits too. Just don't get sucked in to the excited buying frenzy.