I don't think that your daily coffee transaction needs to be on the blockchain. I don't think that every node in the entire network needs to process, verify and store your coffee transaction until the end of time
For that I will evaluate the cost of a node and then the cost of storing a transaction on the blockchain. Lets assume that our example node is a Raspberry Pi 3 Kit with power adapter and case (50$ on amazon) and an external hdd (4Tb - 110$ on amazon). That would be a total of 160 $. If you want a different configuration you can extrapolate the costs at the end. As additional costs I will evaluate power consumption for running a node for 5 years and add that to the cost of operating the node (2.4 watts for 5 years gives us ~100KWH and a total cost of 12$). Total price of a running node for 5 years is 172$. If you read this I will assume that you have internet connection and that a running node on a decent connection will not impact the performance of the network.
At the moment of writing this post the blockchain is 106 Gb in size and contains 204 mil transactions in total. My node has a total of 4TB space available so no matter the blocksize it can store ~8 billion transactions.
A single transaction would cost my node 172$/8bil=0.0000000215$ or 0.00000215 cents. Lets see how much it costs to the entire network. ~6400 nodes x 0.00000215 cents = 0.01376 cents. To give you perspective, 72 transactions would costs the network 1 cent. Even if I double the cost of my node (for those who would say that not everybody runs raspberry) that still gives us a total network cost of 1 cent for 36 transactions. And for the skeptics out there I will quadruple the total nodes cost to 1 cent for 18 transactions. If is that cheap to store transactions onchain is it wrong to ask why bother with offchain at least for the next 5-10 years?
TL;DR A transaction costs in terms of resources used on the entire network 0.01376 cents! (or 72 transactions for 1 cent). In reality users pay more for a transaction because they pay the miners for securing that transaction, but the actual cost for the network to store the transaction is extremely cheap.
