Seems the cheapest about
MS PRO Duo = Sony PSP
Sony PlayStation 3
All devices with a Memory Stick PRO Duo slot
The SanDisk Gaming Memory Stick cards turn the PSP (PlayStation Portable) handheld game device into a fully loaded multimedia entertainment unit. It is the Must Have cards to save your game data, listen to digital music, play your favorite videos, and view your favorite photos. You can even download games from the PlayStation 3 onto SanDisk's Gaming Memory Stick and play them on your PSP. SanDisk game cards maximize your world of entertainment!
SanDisk game cards utilize exclusive MLC memory and controller technology developed at SanDisk, meets all Memory Stick specifications, and is guaranteed compatible.