I dont think deidara costs that less. He should be around 15k to 18k, i suggest you to save 20k coupons and wait for Fuku rebate, maybe you will get him in that event for free. In anycase i suggest you to wait until u get 20k coupons and wait for coupons rebate, you can easy get 2 ninjas or even 3 worth 15-20k each :)

There is an event called "Fukurokumaru's Deals" where you spend your coupons/ingots and you'll get items/rare ninjas back based on how much have you spent. Like this week: f you spend 20k coupons you can get 80 frags of jonin minato and a lot of other good staff. I remember when Angel Konan was released, i spent 20k and i got 80 frags of edo deidara from Fukurokumaru's Deals rebate :) If you are a f2p or a low spender i suggest to save your coupons and wait a good opportunity to spend them!