Aspley Heath Jubilee party June 4th

We are having a garden party in Aspley Heath (MK17). There are 4-bands each of which have their own PA system, but it would be more effective to have one single larger PA system they can all use, and a sound engineer to do set up and facilitate changes of bands and mixing. We would need a minimum of 3 DI boxes, 2 instrument mics and one vocal mic. I would like to know the approximate cost of a suitable system (say 500W) and an engineer for the day 10:30 set-up and party 12 -5PM.