Any designer worth the name will talk you through a whole lot of possible options in plain English.
The moment they begin to confuse you or fail to make each facet of your project outline absolutely clear in understandable language, cross them off your list and find someone else.
You should find that any good design house/team will run an evaluation based on what you think your anticipated use of the site will be combined with how they believe they could deliver it in its most useful, successful and usable form.
Without knowing what you intend to do with the site (selling, information delivery, providing downloads, gathering information from users through forms, processing orders which is where dynamic databases will come into play and so on) no designer can really give any indication of cost, appropriate script/language choice and so on. Again, if your needs, requirements and expectations are not fully explored, find another designer.
In brief you need to know:
1. Final cost broken down on a feature by feature basis. What are you getting for your investment, what was the rationale given for suggesting the final solution(s) for your web, will the proposed web meet some or all of your own requirements...
2. Renewal dates - is your domain up for renewal or if it is a new registration, how long will your designer register it for you
3. Who owns the domain ? I can't believe that some design firms register client domain names themselves and hold ownership of them, but it does still go on so make very sure that your site will indeed be yours and not registered on your behalf and held for you.
4. How much are updates - this will vary for images, text, database content and so on.
5. Time to deliver and date to go live. This is important and should be made clear once talks become serious. You need to know when your site will be functional and your designer needs to know when you need it. A compromise between the two is normal.
Things to ask yourself include:
Do your need dedicated POP3 email accounts for your staff ? This means you @ yourdomain . co . uk
Do you plan to sell online and will this selling require a product catalogue and secure credit card payments or will transactions be processed using company account details with no recorded card details.
If you plan to process client details, are you already registered in terms of Data Protection ?
You should provide as much information as possible to your designer (printed media, catalogues, brochures, letterheads, business cards and images) about you, your business, its products and services, staff, premises, portfolio or client examples and so on. The less work the designer has to do, the less expensive your project will be and the quicker it will go live. Editing raw text, doing photography and image processing and so on can soon mount up and make a site total cost skyrocket.
There are other questions you could ask, but perhaps if you offered some details of what you and your company do and how the site would be used we could come up with a more suitable list since the above is very general.