Tess is dead on (I keep saying that! <grin>)
If you're going to pay for any designer - you have to take the time to know enough about good design to make the right choice. It's just too critical to your success.
You have to think of both sides of the coin - visitors and search engines. If you have ugly code, not CS3 compliant - neither Google nor visitors will find it usable.
IMHO - WordPress is amazing for blogs. If you want a site that you can edit without having to know HTML that will be scalable with tons of functionality and good
SEO - you need Joomla.