test the permissions of a web app

Hi I have quite a big web app
with many pages and different levels of permissions
(and groups)
and I'm looking for a security oriented consultant for the tedious task of manually checking for 'leaks' of data:

you should inject/spoof the various get/post/ajax parameters
and see if you can access data that you are not supposed to access.

Please bid only if you know what we are talking about :)

Thank you.