Which Is Easier To Convert - PSD or HTML To WP Theme

I have my eyes on a theme that I really like on a third party site. I will start off by saying, I do love many of the themes here and have used them for many a project. However, this one is specific to my project and looks great for what I need, thought I might be able to save a little time in the customization department by using it.

The issue is that this specific theme is only for sale in HTML and PSD format. Does anybody here have any suggestions on a "good" company to do a conversion to a Wordpress theme and would it make more sense to the developers if I had them start with one or the other?

Secondly, is there anybody here or suggested for such work?

Thanks for any input you may have,

Nick