The most cost effective way to get big double pane windows is to buy sliding glass doors and build around them. I made the mistake of buying huge vertical slide windows because I thought they would look better. They were considerably more expensive than sliding doors and the counterweights don't have enough pull to hold the windows open. So they stay permanently closed. I hate these windows so much I considered replacing them with sliding doors.
If you are worried about appearance you can put screen frames in front of them and nobody will notice.
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