Two things >> volume and customization.
Volume is simply the # of pages on your site. All things being equal, a 10-page website is going to be less expensive than a 95-page site.
Customization can mean ...
Custom content. Do you already have written content for your site or does it need to be developed?
Custom design. Do you want a highly unique or unusual layout for your site that requires re-engineering the underlying site structure?
Custom images and graphics. Do your images and graphics require specialized Photoshop effects, above and beyond standard cropping and resizing?
Custom programming. Does your site require integration and rigorous testing with a 3rd-party application like a shopping cart or client scheduling system?
It's fine if you want a high degree of customization. Just understand that it increases the cost of your project.