That is a total ripoff. I’ve had bigger cuts than that fixed for under $100. Ask any of the local luxury car dealers who they use for reconditioning on trade ins and then call them directly.
Follow-up: used a sliver of wood to apply a drop of “Loctite Vinyl, Fabric & Plastic” transparent flexible adhesive to underside of the tear, and being careful not to schmear any onto seat upholstery itself, and then pressed it down in place. Cure time is 30 minutes.
It seems to have done the trick and now the tear is virtually invisible.