Remember he's running a business, not a charity
If it's impossible for you, it will be at least difficult for him. Those donuts, especially when new, are a pain in the [Oops!]. I was going to suggest $100 range, so his price maybe a little high. This spring I paid $350 for a simple, custom cat back system from a local shop (with new hangers ;) ). The one job I will pay someone for is exhaust.