Fairness is overrated. 8TB drives are currently around $150, which prices 10GB of storage under 19 cents. Bandwidth costs would dominate if one peer had to upload the same material thousands of times, but in a P2P system the average peer uploads each thing once, and then we're back to pennies. It's an amount of money smaller than its own collection cost. Do I really care if I'm paying for $0.75/year in local computing resources and only using $0.03/year myself? It's not even worth negotiating over and would generally have still existed and just been idle in the alternative.
Moreover, even if everybody is a scrooge who can't just eat a negligible annual cost without worrying about it, you don't need everybody. You just need a few extra nodes to provide redundancy for you. Which could be your sister and your best friend and your father in law rather than some strangers you have to pay in a way that requires you to file weird tax paperwork.
The fundamental problem is that within a network, resource (storage, bandwidth) is scarce. There might be altruists that are willing to donate resource to the network, but there's a finite amount of them. Using a market to solves two problems: it deters abuse (eg. someone using the network as their personal backup service) and incentivizes non-altruistic people to contribute resources to the network.
I don't know if a peer-to-peer resource trading market and currency are necessary here; the device owner with spare capacity and the business proprietor may be one and the same person, which would simplify the situation a great deal.
You have a cafe/small business owner who already owns a smartphone: that device has a decent chunk of data plan allowance, CPU and memory.
They'd like a small site to promote their business online; so they install the web server app and it allows them to add, edit and publish basic content - a few images, some blog posts, etc.
Self-hosting like this means they don't have to sign up for a monthly subscription, their users aren't subject to any tracking (assuming there's none embedded in the content generated by the app), and service provision scales until they need to upgrade to a dedicated host.
The questions about radio and battery usage are totally valid, so perhaps those need more consideration (user superkuh has some suggestions there).
In short: the resources and capacity already exist and we've already paid for them. The question is whether we can re-use those rather than being sold more of the same.
Using pricing to mitigate abuse is only necessary if you're not doing anything else to mitigate it.
Imagine a collection of independent storage pools managed by various entities that control access, e.g. the IT guy of your family, your employer, some free software collective, some small business association. You join one (or more than one) based on a referral or personal relationship or whatever criteria they want to use. Then you have an account with a quota in excess of what any ordinary person is going to require but which doesn't allow Bob to dump 500TB of garbage into the pool without first negotiating with the administrators.
At which point the altruistic donations, i.e. the idle capacity of the devices of everyone in the pool, are enough to handle everybody's non-abusive workloads.
Moreover, even if everybody is a scrooge who can't just eat a negligible annual cost without worrying about it, you don't need everybody. You just need a few extra nodes to provide redundancy for you. Which could be your sister and your best friend and your father in law rather than some strangers you have to pay in a way that requires you to file weird tax paperwork.