Cytus 2 is currently having a limited time sale till on all the in-app purchase characters. The sale is for all 9 purchasable characters for $35. Normally they are $10 each (excluding Miku), which would be $90 if you bought them individually. So it comes out to a little less than $4 each. The sale is only for another 15 hours from now.
They are also running song pack deals for $2 each. They normally cost $5. This sale is until 4/14.
Link is only for reference to the game, but the deal is posted on their facebook page.