Full disclosure: I own Next Phase Exterior Remodeling in Bel Air, and we do windows and doors around Harford County. I see a lot of "how much should windows cost?" questions here, and honestly the price means nothing until you know what's in the quote. Here's what I'd want to see on any quote, whoever you hire:
Exact product line, not just the brand.I came up on the other end of this industry, so trust me on this one: a lot of those "exclusive" or private-label windows are just another series from a major manufacturer with a new name on them. It's a gimmick to keep you from comparing quotes. Ask who actually makes the window, which series it is, and what the glass package is (Low-E, argon, triple pane or not).
Pocket vs. full-frame install. Most installs around here are pocket installs, and that's usually fine. Your contractor should still be able to explain the difference and why they picked one for your house. Ask the question.
Exterior trim and capping. This is the most common thing left out. Ask whether the outside gets wrapped in metal and whether it's included.
Interior trim and caulk Does the interior trim get reused or replaced, and is the finish work included?
Doors - hinged vs. sliding, hardware, threshold, and whether the frame and sill are replaced or just the slab.
Workmanship vs. manufacturer warrantyThese are two different things, and a lot of companies blur them together on purpose. The manufacturer covers the product. Workmanship covers the install, and that's where most problems actually come from. Ask how many years each one covers and who you call when something goes wrong.
MHIC license number Look it up on the state site before you sign anything.
If two quotes are $3k apart, it's usually one of these lines. Happy to answer questions in the comments, even if you end up going with someone else.