Remove all units, remove washing machine, remove sink from old worktop, cut new worktop, fit sink, cut back/extend waste & water supplies, refit units, fit new worktop, connect and test. A day's work and because the space is limited (especially when you've got both units in and you're crouched down trying to work between them doing the connections) I'd put a bit extra on top for the ballache. That would include materials though to be fair, and allowing for the replacing of the inevitable broken tiles when you remove the worktops.
*EDIT* Just re-read your post, you want the worktop replaced both sides? Yup, I'll stick with £500 easy, although it may be less up your way: I'm working on SE prices here.