Here's something that may help ...
-Is it a Fixed bid job (one-price) or Time and Materials (hourly)?
-When do you need delivery by?
-New Project, Facelift Project, or Major Overhaul?
-How many pages of content are we talking about?
-Any dynamic content feeds? Database?
-Hybrid of Flash and HTML, only HTML, or only Flash?
-Flash Navigation, or the ability to switch between both?
-Administrative tools for performing updates?
-How many graphics?
-Do you have your own graphics?
-Do you want to license Stone images or Comstock images?
-Is your content written and/or will be available?
-Who's building the back-end?
-Collaborating with your team?
Those are the most important questions to ask (and obviously it was customized... but you get the drift). You already know the answers to most of those, so the less "helpful" the client is, the more you charge. In general, you don't want to be tied to a project after you complete its design. What you can do is create a "web administrator" but this is not possible using HTML alone, so you'll have to get creative (dynamic web languages) and charge for it as well. Tell them it's better than "employing" you to do it every week.
If you decide to charge a flat fee, you obviously don't want to short-change yourself if you end up doing something that takes 1000 hours. At the same time, if you charge an hourly rate, you better be good at what you do, because those hours can add up if you "play" around too much. It's always a tough call, and you have to see what the client is willing to work out with you... based on the answers to the above questions.
As a general guideline for myself, I don't charge individuals (non-company-related) any more than $1k, because it's unlikely anyone will be able to afford it. This is freelancing, after all. Dynamic / Flash sites will reach this, as it demands about a $75/hr rate, but I don't go crazy with it. It can easily become more work than you, as the freelance developer, bargained for. Straight up HTML sites go for $500 or so. Draw out a statement of work in the contract beforehand, so the client knows adding things after the fact WILL cost more money. Again, those are just some of the things I personally go by... your sister may want to be "nice" about things, but I've learned that people will pay for good work, regardless. Hope it helps.
