Prices typically match prices of games in your local store. They need to keep bricks and mortars retailers happy, and apply your local taxes, etc.
But in answer to your question, yes, you can take advantage of the economic differences by buying your games from certain foreign markets. You will need to create a US account, and buy US PSN vouchers (or use PayPal via the PS web store) to buy games. For PS Plus, you need a credit card and a legit US address though, so that may be an issue.
My best guess you're in Australia. Big W had Ghosts for $68 not too long ago. You might be able to find a similar deal in the near future if you keep an eye or two out.
I'm from the UK and the prices are utterly absurd on the PS Store, so I've chosen to strictly stay away from it and not give the those greedy ass publishers the satisfaction of milking that extra money from me. I find going to a price comparison website like idealo.co.uk, searching up the game title and there you have it. You've just saved £10-15 on each game purchase. Granted this wont always be the case, in which case I'll just wait for the game to go cheaper.
Take it up with your local retailers and your government. There are far too many factors involved. The value of your currency versus foreign currencies, the domestic value, inflation, the cost of doing business in your country, higher wages, higher living standards, higher taxes (including taxes in advertised price - Remember in the US its advertised price + sales tax, as taxes vary between states.)
The reason the cost of a game in your country has BIGGAR NUMBERS LOL than the price tag of the same item in the US, is not because the demonic armies of satan are in charge and want to molest your nephews. Its because you live in a different country with an entirely different economy, entirely different tax system, with (probably) better wages and living standards than those rapidly declining in the United States.