I am not interested in quoting but have a suggestion/question:
If I was doing a part similar to this I would possibly do the fins on a milling machine using a slitting saw interpolating around the OD. It would be trivial to do this and make a 0.25" deep groove.
However your picture seems to show a radius at both the root and crown of the fin; is this correct and is this necessary? If square corners are acceptable you could consider not limiting yourself to a lathe operation.
An open mind is a virtue...so long as all the common sense has not leaked out.