It will cost a gas fee to deploy the dApp, but it's not real money because it's on the rinkeby test network. You can get fake ether from something called a faucet to keep in your rinkeby test wallet. Try this faucet here https://faucet.rinkeby.io/ (there are many others if that one doesn't work)
Curious on your thoughts when doing this tutorial and the one you have on dev.to https://dev.to/dabit3/the-complete-guide-to-full-stack-solana-development-with-react-anchor-rust-and-phantom-3291 ... the linked tutorial is with solana, but I'm wondering which one would be better to get the feet wet with so to speak