I used to do mock ups, but it started becoming a time suck as if I were building the actual site. I've had clients spend weeks just on the mock up and that's just too much for the price point that I'm charging. My rates today are bare bones, based on time and expertise. If I charged twice as much I probably wouldn't mind going through the mock up dance.
Much better for me to do it live (on a build area), and bring them along on the way to change as we go, and them move to the next.
It's also hard to do a mock up that is on target without knowing more about the company and what they're want their website to do for them. Since that's always the initial hurdle, you can end up doing 3 or 4 mock ups before the client gets their thoughts together to figure out who they are, who they're target market is, and what they want to present.
This is actually a perfect example of wants vs. budget and the OP. When your budget is low you have to give up some luxuries and maybe even pitch in to get the price that you want or at least get it lower. I don't think many people who want it cheap understand that they are basically asking someone experienced and knowledgeable to spend weeks with them, guide them, consult with them, teach them, and do a great job on design, marketing, sales, and functionality..and do it all for less than min wage.
They feel that unless you are physically turning knobs and writing code, that all the phone time, marketing consulting, writing, SEO, image searching, and so on..has no value and is something you should just do anyway for free.
Like I said, people who do some research, and come prepared with all of that figured out, written, and a clear direction get the best price and a quicker turn around. Helping clients figure out who they are, what they're doing , and take what's in their imagination and turn it into actual language is 90% of the time suck.
Bookmarks