For your $100 purchase, you can think about Ethereum, DOT, LINK, SOL, or AVAX.
They all have different things to offer. Some give quick processing times, blockchain solutions that can be changed to fit your needs, and other things.
For learning more about altcoins, here are some places to look:
These links will take you to https://coinmarketcap.com/ and https://www.coingecko.com/ .
But always remember cryptocurrency is a risky investment. So before investing go through all the terms and conditions and then invest wisely.