A lot of time on E-lance or other freelance sites you can get great (cheap) prices...but you usually "get what you pay for".
Not knowing the person you hire is a scary undertaking. So, do the best to protect yourself by:
Checking out the person/firm, their work, past clients, and get a written proposal/quote and a contract. You certainly do not want to pay in full until you are completely satisfied. There should be provisions in the contract to deal with if either party does not do what they said they will do.
Hiring a consultant to oversee the work - unless you knnow the consultant - is sort of doubling the problem/potential problem.
There are a lot of scripts / programs already written and available, Id` be surprised if what you want is not already available... or smoething available only needs a little "tweaking" to provide for your needs.
~Roland
I`m a very experienced software developer and I think you`ve been given some really great advice from the previous posters.
I think you should find someone local, even if it`s more expensive. Also, you say that you`re somewhat illiterate with respect to software development ... but you know what you want. [That`s a good thing.] If you`re inexperienced with the in/out of software development, it`s going to be exceedingly frustrating unless you hire a really first rate programmer. Trust me, software development can be interminably frustrating even when you *know* what you`re doing.
If this idea isn`t top secret, post a bit more and I`ll try and give you more specific advice. Private message would be fine as well.
Hiring a supervisor may be worth it only if a/ you know your supervisor well b/ he knows exactly what you needs. If possible he should be someone working with you on your business.
The development of a website requires constant communication between programmer and client: before the project has begun there is communication on the requirements, and several change-approval iterations, during the project development there is communication on possible changes in the requirements due to performance issues, UI recommendations from the programmer, etc. So if the supervisor is not competent enough and does not take the same decisions as you would, then you would anyway have to be involved..so hiring a supervisor becomes useless in this case.
As far as whether a company or a single programmer should be hired: that doesn`t matter, what matters is the experience the person/company has with sites of similar nature. Better find a a few sites you like, find out who built them and contact these people with a request for quote, specifying what exactly you need. Very often companies specialize in specific businesses (e.g sites for media) and do not perform very well on other types of websites...
RE elance: there are some good companies bidding there, but you will hardly notice them as they are just buried among the indian / east european companies..so I wouldn`t advise you to lose time sifting the offers there..
FYI... I`m sure there is already a script (PHP application) to handle that kind of transaction.
~Roland