Which window?

All right, here is the dilemma. I need to replace 23 double hung windows. Two are triple windows, one is a double window and the rest are single windows. All window brick molding will be repaired and wrapped. I live in Northern VA

I have the following quotes:

Okna 500 series deluxe, no grids for $8,500
Serious Windows 600 series for $18,000
Serious Windows 500 series for $14,000
Pella Encompass for $14,000

I know its double the price between Okna and Pella/Serious. Based on what you see, which way should I lean?

A few observations:

-The Okna 500 is the best product of the bunch hands-down.
-Serious has some respectable performance #'s, but I'd still choose the Okna everyday of the week. Serious as a company is barely staying afloat despite millions in federal dollars, so I'd suggest some serious research (no pun intended) on the health of that company if you intend to go that direction.
-The Pella choice is just not very good and should be crossed off the list at any price in my personal opinion. The performance ratings are not in the same league.
-The Okna price is VERY low. Who is the install company? $369 per window completely wrapped and out the door (if I'm reading that correctly) is insanely low for one of the top window choices available. I would be sure to ask details about the installation and thoroughly investigate the dealer.
-In NO VA, the only guy that I can recommend is Windows on Washington. Stellar company to do business with. He would be higher than that Okna quote, but quite possibly the same or less than the others, and you would have peace of mind in knowing that you are dealing with a top-flight installation company. You can get a good feel for his high level of expertise and ethics through a quick search of his board posts here.

Is it possible the installer is cutting corners on the install? Are there ways to do a substandard install and not incur the typical costs that a quality install would?