Anything in the $189 range is going to be a junk window or a junk install. Both will net you a poor performing window.

What area/climate is the home in?

Existing windows are wood with storms, I suspect?

U-Factor, Air Infiltration, DP, VT, and SHGC are what I measure a window by on the performance end of the equation.

+1. At $5500 for 12 windows, that is around $450 each. That is actually a very low price for that THV product, and really a baseline (if not lower than baseline) for what you'll find for a good product installed by a reputable, quality-minded company. THV is not my favorite product, but it is a solid, high end offering and is often sold around $1000 per opening installed.

450 is usually the threshold for quality in my experience. When you start getting lower bids, especially sub 400, you are almost guaranteed to eventually have problems.

Thanks for the response. The area of the country is West Virginia/Ohio area. The original windows are wood with storm windows, the sliders are metal of some sort.

THV are quoting their vinyl/composite enforced double pane windows. The house is stick built with a red brick facade.

That is dirt cheap on that window. If you don't believe us, get quotes on some more high end units. I agree with the above pros, although I'd like say $500 per at minimum.

If I wanted to check a competitor, who would be equivalent.

Also, if I wanted to go a little lower on the price. Who should I look at?

You are at the baseline price for quality product, quality install, and a reputable company with a showroom, accreditations, etc. Go any lower and you will compromise one of the 3, no ifs, ands, or buts. The best scenario to find an abnormally low price would be to find a young company that is trying to get established, or an old timer with no overhead.

I agree with karate guy. You may also want to look for a window installer with very rich parents.
Seriously, you are already at a rock bottom price. Why push the envelope.