To get the most out of your project/hobby, you should do as much as possible yourself.(IMO)
In my experience, the most fun of the project is tracking down parts, and trying to get the best deal possible on them. If you pay someone else to do it all, they will just look in a book or call the parts store, with no real concern of cost.
The other side is, if they quote you a set price, they are more likely to cut corners and use the "cheapest" parts they can find, regardless of quality. Doing the work youself insures you will get the best price vs quality. Not to mention the personal satisfaction of knowing "you did it yourself"
I pride myself on being able to find deals. Most people would be very surprised to know how little I have in my Z, and all the parts to go with it. My guess would be, much less than 1/2 retail.