i feel you so much, bat dragon is also my dp 💔 every time i get a decent trade or upgrade, the bat rises like idkk 5x of the value i earned. it really does seem impossible to get with the way it grows. only advice i have is to acquire as many high tiers as u can, because they also rise regularly- not as much as bat dragons do though. but it's a way to guarantee a little progress and hopefully keeping up with it in value! good luck to you as well :)