Maflu,
Unfortunately, I don't think there's gonna be a real answer for ya. Sites like that can go anywhere from $150 to $150,000 depending on the end product (all HTML pages are NOT created equal,) who you're selling to, what you're promising, and budget!
If you have no insight into their budgeting, it really comes down to what you think they will pay or what are you willing to do the work for.
My suggestion is to figure out how long each page will take to lay out, assign yourself a fair hourly rate, and calculate it like that. Pick a number you can live with, and work on honing your negotiation and pricing skills as you pick up additional clients.
Hope this was helpful - Good luck to you!