How much will I spend to make NFTs?

RAM is required to interact with contracts and in this case to mint NFTs. You will need at least 151 bytes of RAM to mint an NFT. You start with a little bit of RAM reserved to interact with some contracts if you created a WAX Cloud Wallet, which can be used to mint a few NFTs. The value of RAM fluctuates frequently, to check the price see https://wax.bloks.io/. The cost of minting one NFT on WAX is around a few dollar cents, currently.