The PlayStation Now public beta for the PlayStation 4 kicks off on July 31, but the prices you'll see in the store are absolutely not locked in stone.

They're one of the many things that Sony hopes to experiment with during the beta as it feels out what people are looking for and how much they'll pay for it, said Jack Buser, senior director of PlayStation Now.

"We are going to be going into open beta on PS4 specifically for the rental aspect of the service," he said. "These are the early days, so we're always listening to feedback. Over time, new content and a lot of other changes will be based on feedback and usage we'll see in the beta."

Already, the closed beta for the Gaikai-based video game streaming service has helped shape some of the service and what people will see when it's open the public. You can see what the new service will look like in the video above.

For instance, at least one price change is coming. The beta will launch with more than 100 games from more than 50 publishers. The games will cost $2.99 for four hours, $5.99 for seven days, $7.99 for 30 days and $14.99 for 90 days, payable via PlayStation Wallet. Rental periods can be extended.

But soon after the beta launches, Buser told Polygon, the service will start introducing a lower price point, $1.99 for four hours, for specific pieces of content.

"You can expect to see all different sorts of things," he said. "You'll notice different games will have different durations made available. Some will have four hours, seven days, 30 days and 90 days, some will have fewer options. Some will change over time.

"Part of what we are testing is rental duration, pricing and content types."

Buser added that they are also working hard to bring a subscription option as well to the rental service.

Robert Stevenson, central business officer and senior vice president of strategy at Gaikai, said the service has also already seen quite a bit of change in its user interface.

His hope is that the beta will also allow Gaikai to stress test their streaming system, though he's convinced there won't be any issues.

"The streaming network that we're using is a dedicated network just for streaming," he said. "It's connected to the PlayStation Network, but we have servers designed for playing these games.

"One reason we're going into open beta is that we're expecting millions of customers to try this," he said. "We've been gradually stepping up the number of users and we feel we're at a very good level."

Buser said the service has already seen 300,000 hours of gameplay in the private beta, which ran from the end of January until this month.

That's not entirely surprising given that this is the only way currently for PlayStation 4 owners to play PS3 games on their console. But what about those PlayStation 2 and PlayStation games that Sony originally said would come to the PS4?

Buser was quick to stress that the beta was in the "early days" and that anything was possible, but he declined to talk specifics. That included speaking about how the subscription service they're currently tinkering with might work, what sort of other games might come to the service or if Gaikai will eventually support the ability to allow remote friends to take over live gameplay, something shown during the PS4's unveiling in Feb. 2013.

"I think in general during the open beta," he added, "we're open to any feedback."