Agree with JeeWhizz. nearly everything people want to do can be done for free/little cost if you do it yourself, or get someone cheap to do it.
If you want someone experienced to do it, who will question you to make sure you know what you want properly, based on other ideas/aspects, then you will be looking at a start price of £250 per day, but often in the £400-£700 per day price range.
£500 per day eats through small budgets very quickly, especially if you haven't pinned down *exactly* what you want at the end of the project.
A lot of people get angry when quoted £500+ per day for this kind of stuff, and confuse the fact that it can be done for free if you do it yourself with the fact that people who o this as a business need to charge. (like a raging bull!
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But then they haven't been building web applications and sites since the days of Mosaic and seem to think that they should get a special deal because it's them.
From what you say you need, some bits can be done on the cheap using off the shelf freeware, but may or may not cover everything you want to do. My experience of a lot of free software is that if you don't want to do it their way, it's a b*gger to change to the way you would like...
Before you get an accurate quote though, you would need to write a proper spec - even a basic one. That helps you clarify exactly what sections there are, how they interconnect with each other etc. You may want people to sign an NDA before allowing them access in order to quote. Anyone wanting to quote seriously would do this as a matter of course, so don't feel that it would put people off.
Server hosting can be form peanuts to very expensive, depending on how much you feel you can get away with. Avoid shared hosting and go with either a virtual server or a full server - they can be had for under £70 per rmonth now.
Of course you would need/might want someone to adminster it on an ongoing basis. You could either hire people to do that, or do it yourself.
So overall, cost from zero up to £15k or so I guess, depending on your choices.