We should have 3.5" SSD so they can have larger capacities than the 256gb 2.5" counterparts. Price will be the same per GB because 3.5" will use more of the same size chips. It's not the same as desktop vs. notebook HDDs which use different size platters. Big HDD platters cost less per GB. The benefit of 3.5" SSD would be simply to save space in your case and not need an adaptor to make a 2.5" fit in your 3.5" case.