oDesk has lot of WordPress developers that could migrate your site from Drupal to WordPress at low cost. I like oDesk because it takes screen shots every few minutes as the contractor’s work on your job. You can monitor their work very effectively, particularly if you understand the work being done.
In this case if you don’t want any changes to the site, you could easily post this as a fixed price job, which would probably give you the lowest cost. Looking at the numerous other WordPress jobs listed on oDesk is a good way to see how to post your job – a well crafted job post will get you a better result.
On a practical note I would suggest you consider selecting a WordPress theme you would like use before posting your migration job on oDesk. Take this chance to update your site and migrate to a solid, well supported WordPress theme which meets your functional and visual requirements.
If the theme you select needs to customised in any way to meet your requirements, make sure the developer does this via a child theme, so that you can have easy upgrading of the parent theme.