You are better spending money on the internet connection. Does no good to put in a system that a single user can use all your internet bandwidth. 5m is nothing. 1 user watch a hidef movie from netflix needs 6m. 2-3 users just loading normal web pages will likely wipe out 5m.
You need a group of managed AP. Ubiquiti gives away their management software and their AP are fairly reasonable. It does not do everything a commerical system like cisco does but you would blow your budget just buying the controller and not even have a AP.
Still you really need to think about how to increase the internet before you proceed. In the 100mbs range would likely be a more reasonable value and you likely would have to limit certain type of...