There is no cost for storing data on your own IPFS nodes. IPFS is an open peer-to-peer content delivery network where anyone can run a node and be part of it. If you run your own node(s), all the files you store will be around until you decide to unpin them and run garbage collection the nodes. Or until you no longer run your own IPFS nodes.

If you don’t want to run your own IPFS nodes and deal with managing them, you can use a commercial “pinning service” to store your data instead. This is basically a company that runs their own nodes and will let you store your file on them, for a fee.

The cost varies, search “ipfs pinning service” to find providers.