All your graph says is that those coins are less valuable in terms of USD. Transaction costs are specified by the protocol in satoshis, which is the base unit

All your graph says is that those coins are less valuable in terms of USD. Transaction costs are specified by the protocol in satoshis, which is the base unit of Bitcoin. How much you can buy for one satoshi only depends on what people want to pay for it. We call this the coin value. A coin without value is free to transact with. Run your applications on testnet if there are no other considerations.