“Error rate in manual testing is comparable to the bug rate in the code being tested.”—Boriz Beizer.
Why not consider using tools like Selenim and Watir (or Watin)? Why not look at using tooks like FIT, FITNesse, easyb, ...?
The latter tools will force the UI to be as thin as paper, meaning, will push the business logic to layer below and enable automated tests.
You can realize this using patterns like MVP or Model View Presenter pattern.
What seems to be lacking is either the realization or the motivation to automate. I am calling on these testers to get angry if they are testing the software manually.
Testers should focus on authoring tests and not running them—they should leave the running for computers to do, automatically.
What's blocking you?