PCB service costs? (Board-only vs. Fully Assembled)

Every now and then, there's some good reasons to have PCBs for a home project made by a company. (Time, IC package difficulty, etc.) To understand the expense involved, I'm here to ask:

Have you ever sent a PCB design out to be printed (with or without components)?

What are the minimum and typical costs?

Just for example, let's say it was a 2 layer board smaller than 3" x 3" (76mm x 76mm). And 50 components or less (PDIP, SOIC and 0805 SMT).
How do they get the components? Do you provide them?

In general how does the price of having just the PCB done compare to having it fully assemblied? (x2 the cost? x3?)

**broken link removed** can give you an idea, for just a few boards it is not worth the price and where is the fun?
To do mass production quickly from 50 boards+ it becomes interesting. I wonder what is the cost difference between supplying your parts and have them purchase the parts, they probably buy for cheaper but they must make money on parts and charge you for the service.

Mike