I also saw similar crazy prices when I shopped for a replacement window 6-7 years ago. Called actual wood window factory an hour north and they wanted $3500 for wood 28x40, no including install. kicker was that it would also take nine months since they were swamped with business. Owner was apologetic.
Luckily I found a glass factory 2 hours south and tempered low e double glass were $190 each. I really needed 3 windows so I made 4 with a router in my driveway for less than $1k and it took less than a day.
$9k for 8 hours of my labor?
Two years ago a picture window fogged in rental. Again I was getting quotes of $5000-7000. Glass prices have gone way up. 55”x45” tempered double pane low e with 3/8” glass was almost $500. 6 week wait for glass then routered new sash on sawhorses in my driveway. If I do it again I’m buying a router table. Sketchiest part was removing and disposing of the old non-tempered panes.
I really don’t understand why the markup on wood windows is so high. Maybe because high schools don’t teach woodshop any more?