I found two usages for Criftens/Crifty:

"Great criftens! I bought that beast four year syne for five pounds." (1891)

"Eh, crifty!" cried Benjie, "they're a' aff." (1828)

Yeah, no idea what "they're a' aff" means. Whatever beast it was that cost £5 isn't mentioned. But £5 in 1887 is just over £600 in today's money. So I'm guessing it wasn't a tortoise.