Yes, Osprey is more expensive than Chinook (and unit cost+RAF support vs unit cost+PBL vs lease+little gnomes is a whole other can of financial ZZzzzzz - won't go there).
But Osprey is not a Chinook replacement; it's strengths are speed and range (and it does have a decent payload too). Apply that to (e.g.) MEDEVAC/CASEVAC or CSAR and you have a powerful argument for the platform.