Depends on the area and what others are charging.
I get a car or two a week from a local small dealership and I basiclly clean, shampoo and dress the interior, wheels, tires and just wash the exterior for $80. So $50 for a clay and seal isn't bad for regular customers.
The first thing I do is look at what local detailers are charging.
There's really only 2 places that do this near me and one guy does a crap job and uses amrour all or something similiar. But the other guy charges $100 just for the interior and $110 for wash, clay, 1 step, wax, wheels an tires. For both he charges $190. Trucks are $15 more and vans/suv's are $55 more. So he's more expensive.
So I base my prices around him. What he charges fro $190 I'll charge $150-$175. To me that is fair and cheaper. I aim more so to be fair to the customer. I don't want to charge too little and be cheap. I'd rather charge more and give better service. Although being perfect at it is what I want to always do.
But for what you charge for what you do is about what I would charge for the same work. But we live in different areas, I'm assuming, so compare, feel out your customers and what they think. That's what matters.