as these guys say, I agree, except with the price...
I setup my store myself, including the credit card gateway with verisign and my merchant account, for about $850.00 US.
Recently a manufacturer I deal with decided he wanted to set up his own site, but he had no skills whatsoever to do this, he spent $18,000.00 and it took the firm no less than six months to deliver.
thats a huge range in price, and generally I dont think you can get someone else to do it for you for less than 5 grand, unless you dont use SSL or if you have some ametuer do it.
Now, my site is certainly not the biggest and badest, by far, but it has never been hacked (though they try many times per day) and those pesky credit cards get deleted from my DB everyday, and like I said: $800+- (not counting hosting)
I would spend the other $17,200 on google adwords or something.
I guess my point is... if you have the time and the skill, you can do it far under what the going rates are for hireing a team of developers.
one other thing you might keep in mind if your budget is low... I went to my bank with my business license, a business plan, an outline of what I planned to develop and they loaned me $5000.00 without blinking an eye. so, if you have a good plan, your budget does not have to be zero.