I have to agree with pa350z. We have Alenco windows from the early 90s and they have been falling apart for years now. We paid a local glass company (Sheas Glass in Gainesville) to replace the double pane glass inserts. They were inexpensive, (around $125 per window, as I recall), but the company did a slap-happy sorry job on the insert replacements. Especially the 2nd round when we had even more windows going to fog. One window that they repaired requires the Incredible Hulk to raise it up and down, because it is jammed in the frame so tight it doesnt work and this is after the repair job.
Worse, they did not even provide an itemized list of what they quoted me originally vs. what they actually installed, which created a lot of confusion. Plus, they were supposed to do minor repairs on the other Alencos - supply missing parts and that sort of thing, and then didnt.
I will never use Sheas again, and I will not pay another dime on these windows. I am glad that some still work, but we are now looking at having to REPLACE some of the others, like the big window in the Dining room bay that is all fogged up.
Like you, we have to tear off the outer cedar wood trim and probably the T-111 cedar siding to get the old window out, as it has fins on the sides. This does not look like an easy job - but then again, it looks like the price you are being quoted is pretty high.
I guess if I had it to do over, i would get new windows instead of repairing old junky windows. The energy savings alone are probably worth it, especially if there is a tax credit to be had (or use your HELOC and you can deduct the interest). The bottom line is that we wasted about $2000 on 2 rounds of repairs and are still having problems - not just with more old windows losing their seals and fogging up or having parts fall off that can no longer be purchased anywhere, but also the windows that had new inserts are not working because the workers did a sloppy repair job of reinstalling the frames. A house inspector would rip us apart on the windows issue.
I hope I can find a trustworthy contractor to work on our windows. Good luck!