You can still get a high quality (in workmanship) basic no frills interior for a more reasonable price by using regular marine or automotive vinyl or cloth. The problem comes when people want all the time consuming custom extras and can't understand that extra labor means we have to charge more. On top of that, all of us have higher overhead because supplies (especially foam) have skyrocketed in cost. This is certainly not exclusive to upholstery shops, everyone is feeling the pinch and having to raise prices.
If you think car interiors are bad, check out the price of an airplane interior. Everything you use needs to be FAA certified flame resistant, and has to have certification papers to prove it. Leather that sells for $10 to $12 a square foot is double that. Fabric that sells for $28 to $35 a yard is $65 to $80 a yard. The carpet I used in a 1955 Cessna 310 cost me $105.00 a yard, and it was only 8 feet wide.
No one lives forever, the trick is creating something that will.