Many (probably most) residential window contractors are straight up scam artists. Loan sharks would be ashamed to put as much markup on a product as they do. Any invoice they show you from their supplier is absolutely, positively guaranteed to be a complete lie. They’re gonna pay maybe half that.
Are you sure you even need new windows? A draft around the window isn’t a window problem, it’s an insulation problem. It’s solved by removing the interior trim and squirting some spray foam in the gaps.
If they don’t open and close easily that’s usually an installation or building movement issue. Possibly a maintenance issue. Maybe fixable, maybe not if enough damage has been done.
15-20 year lifespan is absurdly low for a window, even crappy ones. If yours need to be replaced 25 years after the house was built it means your house was built poorly with bad materials.
If you do decide to replace them and your Stepford McMansion description is accurate, you probably shouldn’t waste money on wood windows or let yourself get talked into some crazy high end whiz-bang vinyl ones either. Go mid-range from a company you’ve heard of before - Pella, Anderson, Jeld-Wen are all fine for a basic house in the 'burbs. There are lots of companies you haven’t heard of that also make good, affordable windows, but you’re going to struggle telling them apart from the shitty ones.
Low-E insulated glass is all you need for energy in your climate. You’re going to quickly run into diminishing returns for any features above and beyond. Anybody who tries to convince you otherwise is ignorant or lying.
There are replacement windows and new construction windows. The former go into the existing window frame with a few screws and some caulk. If you have drafts and/or building movement issues, they likely won’t solve any problems you have for reasons I mentioned above. No interior or exterior trim needs to be removed to install them. They also make your window opening smaller and may not meet egress code for bedrooms, and if you have any water leakage problems they probably won’t solve that either.
New construction windows aren’t just for new construction and are the preferred but more expensive installation option. The entire existing window will be removed. All interior and exterior trim will need to be replaced. It’s basically starting from scratch with nothing but the hole in the wall the framers made.
The window unit for either of the above will cost about the same - maybe $3-400-ish for something like a 30"x48" unit. An experienced installer can swap out a replacement window in less than 30 minutes. A new construction window can take hours of work for each one.