This is more or less the way I’d go. It’s “what the client asked for” versus “what solves the client’s problem”. You don’t need to find the bill within minutes,

This is more or less the way I’d go. It’s “what the client asked for” versus “what solves the client’s problem”. You don’t need to find the bill within minutes, you need to know that you _have_ the bill quickly. Grab a big binder, half dozen packs of dividers, a pack of loose leaf paper, and a box of pens. Divide the binder into ranges. In each range use a separate piece of paper for the next digit. Don’t worry about sorting past there, just write all your serial numbers down. Now you can use the dividers to narrow it down to around 2,000 bills. Flipping through ten pages to find the next digit you’ve narrowed it down to about 200 bills. You can probably scan two hundred numbers quickly enough.