Web on Sprint

Okay, so I looked all over the Sprint website, and it's no help. My boyfriend has the Sprint plan where him and his mom share 900 mins a month, with unlimited text and picture messaging. And he wants to know how much it would cost to add web browsing to his plan and how much it would cost a month. They are on a two year plan, so they can't switch plans. They can only add-on.

You're talking about the everything data family for $129.99/ mo.
This upgrade will restart your 2 year clock.

Yeah, that's pretty much your only option.
The other one would be to trade your plan with someone else like on Cell Trade USA.