The final cost will depend upon what your requirements are. What functionality will your website need? Do you have a similar existing site in mind to you wish to replicate?
it may seem like only a little amount of money but you'll be surprised how quickly it adds up. in the process of starting a biz. legal fees are astonomical
do you have a certain script in mind, can you design? what is it that you are not able to do, and would need to pay for, besides the legal and mandatory start up fees, example, merchant account(if need be)