Hi
What is cheap and free exchanges to list a token ERC-20?
its free if you add your token in decentralized exchange such as etherdelta or forkdelta my friend
just drop the contract address from your tokens
here the example
https://forkdelta.app/#!/trade/DAI-ETH
just replace
DAI with the contract address from your token
easiest way could to do for developers that have no fund to pay listing in reputable exchanges. but its so funny if they have no fund to start project and operate it including about exchanges. dev team must concern about exchanges, investors usually compaint about it, so when they see token listed in forkdelta i am believe their trust will decrease and prefer to sell.