Some people just don’t get it: web design alone doesn’t make for a good website. And SEO alone will push a website high in the SERPs, but it doesn’t mean that a site is good just because it appears in the top 10 search results! SEO and Web design should be treated equal.
There are people who are quite skilled in design, but they know close to nothing about HTML coding. Some use the cheapest software to “design” websites and the final product might appear aesthetical when showcased online, but if the search engines are unable to scan it correctly chances are that that site will never perform well in the organic SE results.
If you have a good designer but you also want a good code (and you should), look for a web coder who can transform your design into W3C valid code, using (preferably) table-less CSS markup and making your future website compatible with Firefox, IE, Opera, Safari and other browsers.
The coder should not ignore any accessibility issues either.
Each professional has his/her price. Companies like PSD2HTML offer such services for a flat rate (price per page) and even discounts for each additional page. Other companies will make you different offers, depending on their pricing policies.
No matter what you choose, make sure you have your site SEO ready. This will help a lot in your future SEO campaigns. The SEO company you’ll employ will not have to waste precious time, money and resources on correcting your HTML code. The SEO company will focus on more important SEM strategies instead.