Back in high school, I was a much more active currency collector than now. Unfortunately, I didn't have much cash to spend on the hobby. Collecting complete sets with top condition notes was out of the question. I had to get creative.
Instead of getting excited about having old, rare, historic, etc. notes in my collection, I enjoyed the thrill of the hunt - older notes, fancy serial numbers, printing errors, and star notes. Star notes were my favorite. Here's how I did it:
How to Find Collectible Currency Affordably
Step 1: Save Some Money
First, you need a reserve of cash to work with - "trading money." It could be $50, $100, or $1,000+. I typically had $100 - $200 of trading money on hand.
Step 2: Convert To Small Denominations
Take your trading money and convert it into small denominations. On my way home from school, I took my $100 - $200 in larger denominations to a bank and exchanged it for a pack of $1 or $2 bills.
Step 3: Pick Out The Good Notes
Scan through the pack looking for anything interesting. I mostly looked for star notes, series 1988A and prior, and fancy/low serial numbers. Some of the notes I kept were nearly uncirculated, while others were rags. I enjoyed the hunt regardless.
Step 4: Convert To Large Denominations
Replace any notes you took out of the pack with spare change, so you can convert to larger denomination notes evenly. Visit a different bank than the night before and deposit the small bills into fives, tens, or twenties. Of course, I'd check these for interesting notes, but I didn't nearly have the same success as with small denominations.
Step 5: Repeat Indefinitely
The beauty of this system is that all it costs is time. If you keep a few notes from a pack, you just need to replace them with normal notes from your wallet.
1) Open an account with the bank
Not all banks were happy about taking $200 in singles and converting it to large denominations, or visa versa. Being an active customer of the bank helps avoid being hassled about your request.
2) Ask tellers for help
Bank tellers handle countless notes per day. Asking a teller to help you look for collectible notes may be the easiest way to build your collection. Keep it simple, though. Ask if they can set aside notes with serial numbers that end in stars, notes where the seals aren't green, or notes of the "small head" design (e.g. pre-series 1996). It helps to be friendly and occasionally drop off snacks as a way of saying "thanks" and to encourage them to continue helping.
I didn't keep records of how many notes I searched and what I found. It was a LONG time ago, too, but I'll ventures some very rough guesses.
Notes searched: ~5,000
Star notes: 1-2 per pack of 100. Mostly common notes, with occasional short-run stars.
Pre-1988A notes: 1-2 per few packs
WheresGeorge notes: < 20 total
Error Notes: just one
Two of my favorite finds that I know came from this method of hunting: