I would recommend you decide what type of gun you want before anything else, M4 or MP5. This will make your decision easier.
All guns are over priced in Canada (compared to Asia and the US) but they are in the process of coming down in price as we speak.
M4's are quite common so they aren't bad starter guns as there are many people who can offer knowledge on fixing and upgrading them. You will have mag compatibility on the field with most players if you or they run short on ammo.
The King Arms M4A1 is highly touted as an excellent value for the money and a great gun to start out with. Good quality full metal externals and solid mauri compatible internals out of the box. They retail anywhere from $250 - $300 these days and I could tell you where to get one if you get yourself age verified.