I would suggest you to buy something like 5 bitcoins when the Bitcoin price is 280 USD, and sell 4 of the coins when the price is around 350 USD,
5 X 280 = 1400
4 X 350 = 1400
so you will get 1 btc free of cost.
Your calculations are fine so far.
The only thing you have to do right now it to wait for the price to decrease.
But how do you know it will go down that much?
As halving is coming closer and closer the price won't go down more that much.
Maybe the next few weeks during this month due to christmas we might see a small drop.
With the beginning of 2016 however I expect the price to go up.
So if you don't want to gamble just because of 50 bucks or so I would start accumulate now if you have some money left.
And if wanna make some nice profit wait for halving.
If you should be in for long haul, just hodl!