Crypto supports fractional amounts, so it can be as small as you like. There may be limitations imposed by the exchange itself. But you will be transferring between your exchange account and your wallet - so it's not going anywhere anyways.
You can practice transferring between the exchange and your wallet, and even between two of your own wallets (pretending that one of them is the vendor). It's quite fun, actually. Exodus makes some cools sounds when the crypto arrives

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Keep in mind that every transfer costs you a miniscule amount of "gas", but it is usually measured in fractions of cents. This is the fee you pay to use the crypto networks.
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