Sony recently announced their game streaming service, PlayStation Now. Sony hasn't mentioned the price to rent games. An image that was previously on Gaikai's history page, and has since been removed showed that the price to rent Uncharted 3 is $4.99, and the price to rent Far Cry is $5.99. The price for the full game on the Last of Us, which isn't offered as a rental is $49.99. It has not been revealed whether or not this is the cost to purchase the game as a downloadable copy which would mean PSN and PS Now would be integrated into one store, or if the $49.99 is the cost to permanently have access to stream the game through PS Now. The duration of the rentals has not been revealed either.
As announced earlier, Sony plans on having the service released by Summer 2014.