If you will be a project manager, means the museum is on-going of construction. the salary range for that is more or less 30k (package).

but if you will be a manager on a museum that your job will just stare on those collections display on shelves. you ca ask 50k or more. as it is very hard to do nothing...imagine, you will wait for the sculptured 200 yrs old horse to blink his eyes. :D