man, people's google skills suck worse than mine if they can't find an m4 in canada for that price.
I hope 300 isn't your total budget. You may need a battery and charger... add 60... goggles add 60+.. extra mags.. add another 50... and whatever other gear you may need, boots, hydration etc... it's possible you have some of this already, but at least have it budgeted.
And chances are depending on where you play you'll need to swap the spring to conform to field regulations. 5-10$ plus labor rate.
I project a startup cost closer to aroune 700$ for all the necessary gun/safety gear.