It all depends on the coins you wish to stake!
As the poster above asks, the minimum is arbitrary to the user, and staking a sum should be substantial enough if it is genuinely worth the effort because I don't understand why you would want to stake $300 with a 5% APY. I believe that amount might turn into thousands of dollars in crypto, but doing it for bitcoin right now, it's not worth it. Instead, keep your coins in your wallet, and if you have more than $1000, acquire a hardware wallet for your security's sake.