kenn, good question.
I would ask it a little differently:
How much does one save by doing their own bottom job?
Really. Can someone do the math for me? Savings on two gallons of paint, then labor.
In all cases, it would seem that the haulout fees, bottom pressure wash, and the environmental fees, would be exactly the same.
If that's the case, and if you agree, then what are the real savings. You can also choose to include or not the "value" of your own labor.
I look forward to learning about the economies.
I think the answer depends a good bit on your abilities and your ability to make efficient progress in a workman like manner. I have added it up, and I figure the savings comes to about $80-120 per hour, depending on the sort of project, after taxes of course. I let them haul and power wash. I've never had a problem managing sanding hull prep (vacuum sander), a coat of paint, 4-5 hours of other projects (last time I replaced a water pump, installed a teak cockpit floor, and added two FRP wear plates above the props while the paint dried) and lunch, followed by a second coat in one day. I don't fiddle around, I have all of the tools an skills professional has, and my best interests in mind. It is about being well organized and good at the crafts. I seriously doubt the marina staff could do a better job in less time, and they mark-up materials (which is fair). I've been practicing for many years on many boats, as well as many engineering projects.
For others the math will be different. If you make better than $100/hour after taxes, only work on your boat if you like to. Actually, given a choice between working on the boat (most projects) and watching TV--or being on the internet--I'd work on the boat. It's a hobby, and even bottom painting is relaxing. By all means, if it's a drag (you will never see me strip the bottom, for example) let some one else do it. I don't really work on the boat to save money.