NFTX is a permission-less system that doesn't charge anything to use. There are gas fees involved in setting up your vaults and creating your liquidity pools, but NFTX doesn't charge anything for these.
@ 120 GWEI the estimated gas cost would be:
Vault creation: 0.15 ETH
Mint & stake (20 NFTs): 0.56 ETH
Sushi pool creation: 0.4 ETH
Approvals: 0.05 ETH
Total: ~1.16 ETH for the Gas transactions
You will also need to supply ETH as part of the staking process. If you the NFT floor value is 0.1 and you are staking 20 NFTs then the you will also need 2 ETH to add to the pool as part of that transaction.