You can get asuma wb frags from chases and survival. Theres no point buying them.

This is from survival and chase only. Maybe 20 frags from random pull, still not worth wasting resources on getting him. Just wait a little longer.

Save whole month for lucky board and if there's any redeemable that you want (ninja, charms) then use it at that time. If you have any future ninja you'd like to have, usually it takes about 5months of saving for 15k priced ninja, so research a little and save for him. Same applies to current ones like minato, masked, deidara etc.