Hi all, I'm new around here and had a windows question!

We're looking to replace the windows in a 60+ year old house. We've gotten several quotes and I'm now trying to look into just buying standard windows and having someone build out the house to fit those. My question is, are the standard windows you buy at a home improvement store any better or worse than a custom window bought from a window installation company? Will the labor end up costing me almost the same as custom windows?

To give some sizes, the majority of the windows are 70" wide and 36" in height. I'm looking at getting vinyl sliders.

Also, I live in Hawaii, so rust is a serious issue and I'd need to get stainless steel windows.