Agreed with the others. $20? That'll cover your materials at least. It takes me a few hours minimum for a basic size window (wood interior/clad exterior) and simple stain job (meaning no washcoat or toner coats since the rest of the windows/woodwork usually aren't finished that way.) Included: strip down what I can (i.e. hardware, weatherstripping), cut and remove the caulk squeeze out on the sash, tape off, sand, stain, 3 coats WB poly sanding in between, pull tape, and clean-up including the glass inside and out. I use SW or BM waterborne poly because I can spray it in the shop and brush it on site. And those particular products self-seal. Around here, your basic stain job is just a stain then clear coat. I do get into more extensive finish schedules when necessary, i.e. washcoat, toner coats, etc. But that is not the norm.
During the winter months, I'll finish the whole window, then just stain and 1 poly coat on the trim. Then install trim, fill holes and hit it with the final poly coats to seal the putty. The problem with installing then trying to finish is there are places on the sash and frame you can't reach without opening the window.