For me, cost is secondary.
I need to see testimonials and a portfolio of previous clients. Is my site going to be a unique design that a designer will convey my thought process, or does the portfolio have a certain standard look and feel to it, which smacks of back bedroom template tweaking.
In theory, you shouldn't be able to reconise a designers work, because each one should be a different style and theme.
I agree with Stavros, SEO is a much bigger factor. In the old days, SEO was seen as a bolt on after the site was built, but nowadays it needs to be crafted into the design stage. Such as the postion of content, headers, any adverts. Stuff that moving afterwards will spoil the design. Thought needs to go into page structure, naming conventions, after all, page titles are the SEO number 1 and a bit of a pain to change retrospectively!
Post design SEO/SEM is where an SEO company gets engaged, and if the design is upto scratch, then it should be mainly leg work and off site, ie link building, article writing etc.
But also important to me is communication. If a project isn't shaping up as I imagined, then I need to be able to contact the designer, as well as try and articulate my thoughts. Most people engaging a designer are doing so because they can't do it themselves, so a good rapport and confidence that your designer understands where your coming from is essential.
Reminds me, I still owe you a testimonial!!
