I will not discuss price on the forum.
Time is the killer for your idea, at least four to six days.
Grinding, cutting, metal forming, tacking into place, welding I will do.
Rust treatment I would leave to you.
The job is more difficult with rust treatment application, naked metal is better.
Rust treatment is flammable and highly TOXIC at welding temperature.
Ask Adam how his nerves survived watching me welding on his baby, and seeing it catch fire in small patches due to rust coat burning out of cracks.

Check with your local community college vocational tech center, the auto body and welding class may be willing to take on your car as a project for materials cost, I doubt they get to play with many Mercedes Benz.