I think Sasori would win high difficulty, seems as Hidan wouldn't be able to do anything because his blood ritual, well, requires blood, something that Sasori lacks, so I believe that Hidan wouldn't be a big threat, quick scratch of paralysis poison as Hidan is also one of the slowest people whilst wielding his TripScythe thing. As for Kakazu, his iron skin would make it difficult for Sasori to use any poison effectively, but I think that his collection of 298 puppets may be able to hold him off and even force him to use his hair ball form, in which the third kazekage's puppet will end up destroying him with iron sand. Although this seems like an easy battle, I put it at high difficulty because of Kakazu's experience, and general skill would challenge Sasori.