I had windows that look similar to yours replaced with custom made inserts.

The mold maybe from condensation and or low air circulation.

Maybe $700/window ~5 years ago. 8 windows, 2 patio doors, were ~$11k. Ground floor access.

Those look to be probably 30+ years old, aluminum or possibly mechanically fastened vinyl, aluminum box spacers, possible seal failure in the glass, and some possible issues surrounding the frame in the opening as well.... Anything CAN restored, the question is whether it should and at what cost. These should not and would likely push close to the cost of new window but with obsolete performance if you did.

As for cost, that is a moving target. Where are you located? What grade of window is going in? What type of install? What is the exterior wall like? What window options? What damage is surrounding the windows that needs to be addressed as well? Are they ground floor, or is that a 5th story balcony with some that are not accessible from said balcony? .... You get the picture. The $700 mentioned above is not out of the question, but is likely a starting point if all of the above is pretty basic. Start adding a bunch of options and complications and it could double or more.

Best thing is to research good products and find a good local company or two or three to have out for an estimate.

My old windows were aluminum frames, the technician broke out the glass, inserted “inserts” applied trim. The old frames were left in place.

Similar or same as Anderson Replacement in my area.

Have you checked into the hurdles you have to clear in order to replace the windows given that this an apt. in a coop? You may be limited as to selection & installers...

Repairable original wood windows made with old-growth lumber, as used in houses up to nearly the middle of the 20th century, are usually worth saving and refurbishing if they're not too far gone. Fixed up and properly maintained, they will last another 75+ years, probably close to the life of the house they're in.

But your windows are nothing special. Windows like that are made to last 20-30 years and then be sent to the landfill. It's hard to fight planned obsolescence.

As ci_lantro mentions though in a co-op all the windows need to look identical. You may run up against some push back in wanting to change them. I would find out what your options are from the co-op board then make a decision. As Homesealed mentions 30 plus year old builder grade aluminum are seldom worth repairing but the board may make you go the repair route.

Re requirement for “look”

Based on the photos, identical exterior trim is available in PVC.

How old is the building, I think that window and the windows in the other building were replacements in the late 70’s, and the exterior trim on both buildings have been replaced after the window job.

I would bet the coop building’s windows in other apartments are all in similar shape. Some may be better than pictured, some may be worse. I doubt the coop Board forbids replacement. It is quite likely that the coop Board has already set some requirements for replacement. It might be simply that new windows be double hung. Or, it might be more restrictive, down to which manufacturer you can use and which windows contractor will be allowed to do the replacement. They may also restrict what hours and days the replacements can occur. Those various restrictions will affect your costs. Ask what is the coop Board policy regarding replacement windows.

Building is from 1949, so over 70 yrs. windows must have been changed at some point but probably due for another replacement. I’ll definitely reach out to find out about coop requirements first. Thanks everyone this was super helpful!