Costing a website can be tricky as unless you have spent a lot of time with the client or they have a written specification that you can work through, it is very had to be able to accurately cost the project.
It may be that you can create template packages to offer to customers where you have a list of what is included. For example, many website companies will offer a fixed price for a 4 /5 page brochure website with a contact form. You may even have a website that you are able to show them, that will show what they will be getting for their money. Often people like to see a working product before they part with money and with a website this can be hard unless you have previous works that you can show them.
Be sure to button down exactly what is and what isn’t included in the price and use this to upsell your other products and services. Do not be afraid to find out what their budget is as if they only have a very small budget and it is a lot less than you could complete the project for then you may as well tell them upfront to save everyone time.