There's an ongoing argument that companies like Microsoft and Sony take full advantage of console gamers by charging a membership in order to play games online, one that the PC gaming community often pokes fun at. Whether or not you agree with the membership cost, if you are currently an active Playstation Plus, now is absolutely the time to re-up your subscription.
In the monthly update on the Playstation Blog where we usually learn of the free games this month, a vital update was posted at the top of the page giving the heads up on the upcoming price hike.
Starting on September 22, 2016, prices for PlayStation Plus memberships will change to $59.99 USD/ $69.99 CAD for twelve months and $24.99 USD/$29.99 CAD for three months. The monthly plan will change to $11.99 CAD in Canada, and remain $9.99 USD in the U.S. If you are a current member, the new prices will take effect if your membership renews on or after this date.
So there you have it. There really isn't any explanation for the price hike other than the assumption that they're doing this because the company feels it's worth the value. If you do some scrounging around online, you might get lucky and find some sites that have discounted offers such as from Kinguin, Amazon, or Kinja Deals.
However you do it, though, I would do it sooner rather than later if you're going to continue using PS Plus.