Replacing single pane storm windows in Sun Porch

I am in the process of getting bids to replace single pane storm windows in my sunporch. Currently have 8 really narrow windos and I am considering installing fewer - wider windows.

First quote Renewal came in at about $9,000. That about knocked me over.

Second quote Champion. Went with 6 total windows, full screens, grids on top half. Quote came in at $4,000. Much closer to what I had anticipated - even a bit lower. ...is it too low?

Anyone have any thoughts? Ideas for other windows to review for this area?

I just got one more quote from an independant (well rated on Angies List) contractor. He recommended Simonton Platinum Prism windows. The 7 windows would run just under $4,000.

Renewal by Anderson is out of the picture so now I'm down to Champion windows or the Simonton Prims. Any comments?