Hi Mike,
I have some good news for you; we have a fix!
We've made some changes so from now on the user's language preference, which is built into the browser, will be passed to the report when it runs on the server. That way it would recreate the environment used when designing and previewing in the Report Designer.
You can use this temporary site to show what settings we are picking up: http://web1.methodintegration.com/test/accountpages/TheServiceCoPaulSnow2/LanguageTest.aspx
To change your language preference in IE go to Tools > Options, but chances are it is already en-GB.
You'll need to open the estimate report in the Method Report Designer. To see how to do this you can review this webinar: http://methodintegration.com/cs/blogs/methodblog/archive/2009/09/03/community-webinar-8-introduction-to-designing-reports-level-1.aspx
Delete the Rate field on the report and then drag it back onto the screen.
Once it has been added then click on the field and a little expansion arrow will come up.
Click on the little arrow then click on the 3 dots next to Format String, the ‘Formatstring Editor’ window will pop up.
Select Currency as your category and then click on the 'standard Types' tab and select c2. Click ok and save the report. Try running the report in Method and let me know if that works.