The further you define your business requirements the tighter you can expect your development quotes. This is one of the more time consuming and necessary steps that a lot of people skip. But, if you actually do it, you will be able to minimize the development surprises, get a better estimate on time to develop, get a tighter range on cost. You will also be able to start filtering those that are bidding on your project if you think they`re listening to your requirements, are putting in the time on development quotes that reflect the time you put in on thinking through your requirements, and if they bring anything value-added to the table that you weren`t able to think about.
The stuff you`re mentioning has all been done before so the code should be readily available. But, if you haven`t done so yet, you need to detail, to the best of your ability, exactly what you`re looking for - what the site is supposed to do, every page, every link, will you need advertising space, if so what size ads. You have a product, will you need to store product information, click for a larger image or for more detailed info, if you`re shipping, define your shipping methods and costs, etc. Try to answer all the questions that you`re asking your developer to answer. Draw up a sample screen shot of what you`re envisioning and find websites out there that emmulate what you`re trying to accomplish. Your job is to paint as accurate a picture for whomever you choose to develop it. If you do this - or have already done this, it really doesn`t matter which site you go to find your developer because you`ll be able to better decipher their quotes.
When you get all these quotes, first separate them on who sounds competent to you. Then, start looking at their price. And as vwebworld said, make sure you look at their referrals and past work.
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