There are many reasons why you should do some of this monkey work yourself, other than the obvious, "cost". If you get down in the bilge and look around your eyes and ears will become trained on what looks normal and what is not. When I winterized my boat this year I made a list of things that needed to be done in the spring (hoses that needed to be replaced, a secock that was leaking etc).
I don't do everything myself because I know that if I need my shop to do something in a pinch they will be there for me. So I feed them some work and contribute to the pool.
I am lucky because my boat is a very friendly boat to service, I am a big guy (OK SOME MAY SAY FAT

)and it is very easy for me to get around below. I have been down in the bilge on some of these other boats and must say I would never be able to service these boats and would be at the mercy of a shop.
Also you know when you do it it will be done right and done right all the time, I don't care how good your shop is, it aint the same as when you do it.
Some things should not be done by the inexperienced, you will know what that is when the time comes. As Dave has pointed out, this game (boating) is getting more and more expensive. Hey, there is a guy on this forum "Greg" and he is a doctor, he knows his sh-t and knows how to do it himself.
So I guees my point here is, if your to lazy or don't have the time then yeah, this is what it costs, so stop bitching
Walter