IMO, it's possible those 17 rubles were Anastasia's private pocket money.
Indeed, since as you point out they had little opportunity to spend money in Tobolsk, it would make sense to send Maria off with what they had. She and thier parents were going off to supposedly Lord knows what fate in Moscow , if they were even told that much.
There was no guarantee they would even see them again.
Thank you for the info about the worth of the amount Maria had with her!
