How much would it cost to create facebook?

[Jim Maryland]

You need to realize that the development of a site like Facebook is never really done. Software projects go through a development life cycle and a highly used site like Facebook will be under development to various extents until it shuts down. The cost of developing it has a lot of factors to consider as well. If you have deadlines, you'll need a lot more people (which adds complexity managing those people and what they produce) to meet the deadlines. If you don't have a deadline, a single person could work on it for <X> time as a hobby to complete it.

As for the company that did the programming in your hypothetical question, it all depends on the contract between the purchaser. If I were to pay someone to develop for me, I'd probably ensure that I'd retain full rights to the software developed and that the development company would need to turn over any documents (hard or soft copy) and source code to me. I'd opt to not allow them rights to the code for future use. This may increase the cost to me, so I'd need to evaluate that when deciding to hire.

Hosting can be done by the development company (if they offer that service) or you could purchase your own hosting service for the development company to work with.