The Bottom Line of Web Design
You should go with the web designer that has the best balance between affordable fees and long experience. Your web design firm of choice should have enough experience to justify their fees and your short list of prospects should contain designers you're willing to splurge on for their experience or agencies that have a good balance between experience, quality, and affordability when all is said and done.
The rule of thumb is that the more experience you've got the more money you're paid. This experience pays off in terms of allowing designers to think out of the box and know what a site needs in order to pop or stand out against its competition. There's no bigger waste of money than to pay a designer to design a site that looks just like a hundred or thousand other sites out there. You might as well have just bought a web template.
An expert web designer, as opposed to a non-sentient cookie-cutter web template, is paid for his creativity and problem-solving skills. He can take one look at a mediocre site that's only getting a handful of hits a month, pinpoint its problems, reorganize who its content is presented (since it's usually presentation rather than the content itself that's the issue) and end up with a finished product that should get a spike in visitors in heaps and droves.