Actually if you "stick to the story" there's only 50 dollar bills to choose from and once chosen it's eliminated from the set so 50*49*48*.... = 3*10^64 combinations. Less if any of the bills have identical last digits, which is likely due to the birthday paradox. And if they were just counted and put in an evidence bag most the bills are in the right order. If they count the ones, either in order or reverse order and the only thing you need to figure out is where a few fivers or tens go that's cryptologically pathetically weak. And if it did disappear down some pocket, well there goes your evidence that there actually was a pile of cash making up your password. Worst, the police will probably take this as gloating on your part by showing off your perfect yet obviously constructed get-out-of-jail free card. I think the good old "I don't recall" works better.
If the pile of cash disappears down some pocket, then when you are dragged to court to produce the password, you explain the password storage method to the judge, and the fact that no pile of cash was entered into evidence shows that evidence tampering occurred. Assuming you are in a legal jurisdiction where the rule of law holds any sway, this should get the case thrown out.
If you're in a jurisdiction where this doesn't apply, you're pretty much screwed anyway, (and it's all but guaranteed that your pile of cash disappeared into a pocket rather than the evidence locker.) Granted, in a no-rule-of-law jurisdiction, I'd recommend this method only for data you would literally rather die than give up. The Powers That Be aren't going to stop torturing you once you tell them about your password method, they'll keep torturing you hoping that you're lying and you really can produce the password if they push hard enough. At some point, you'll really wish you had a way to give them the password.
An obvious variation of this is to have a pile of cash that contains 48 bills, with a password constructed from the serials as described, plus something extra you have memorized and inserted in specific spots in the sequence. Then when dragged before the judge, you say that the password was from the serials of the 50 bills you had next to the computer. "What, there's only 48 now? Well, you can try the existing sequence and brute force the remaining digits, but since there are 2 bills missing, there's no way to know for certain where in the sequence to insert the missing digits for the brute force attempt, and since the stack was obviously tampered with, there's no guarantee that the remaining bills are in the original order."
