Right now, my finish of choice is catalyzed urethane, but yes its foul stuff. I spray outside in a makeshift tent, and its pretty evil still.
I've never had an issue with sealers, but I only use shellac, so that may be why perhaps. Pricey indeed, with the catalyst, my stuff costs almost 100$ for a quart. That said on a guitar, a quart goes a LONG way haha. Worth the money imo.
Never seen any that pricey. Even the catalyzed conversion varnish i used to do was like 55 bucks a gallon with a 20$ catalyst you had to buy on top of it.
A quart a long way on a guitar? Have you ever sprayed a full guitar, body and neck? At 3-4 medium coats, you could MAYBE get 2 guitars out of it.