The following advice depends on how desperate you are for the work. If you're just doing anything to build a folio, great, ignore this. If you're past that, read on.
Firstly, never just quote a number at someone. Are you more than a number? Of course you are. If you just quote a number, then all your "client" has to do is compare a bunch of numbers and pick whomever gives the lowest one. If that's how the client operates - ditch them.
Does your client really know what they want? A client who simply says "I want this" (points to someone else's business) probably has no clue what they want or how to make it work, but wants it cheap. Ditch them, they are more trouble than they are worth.
Sell yourself on more than a quote. Sit down with the client and discuss their business needs, what they will use the site for, what their expectations are, what their budget is for marketing, maintenance, etc. Immediately you add value to yourself and someone who is interested in doing good work. If the client isn't interested in that - ditch them, they are more trouble than they are worth.
If you're asking for an idea of cost because you have no idea how to cost it, that's bad for you. Read some articles on how to break down jobs into smaller parts to help you quote. You need to know exactly what you are going to do before you quote on it.
Obviously a CMS is involved here. Which one? Why? What plugins are needed? Where will it be hosted? Is graphic design involved? How much testing is needed? How much ongoing updating / security patching is needed? Make a list of all the questions that need answering, answer them, cost them.
Don't be afraid to explain all that to the client. If the client isn't interested in relevant details - ditch them, etc. etc. You do not want a client who does not know and does not care about the real value of your work. As a corollary, you do not want to be someone who does not know the value of your own work.