Micro Caps have a range of affordable stock exchanges around the world that have reasonable due diligence requirements.  Each one has different requirements for listing.

OTC Pinks - This is the entry level market for the USA that doesn't require securities commission reporting nor audited financial statements

Pacific OTC - This is a recent market based in Vanuatu. Start-ups as well as operating companies are welcome to become Issuers. 

JP Jenkins Share Matching Service - this is a UK operation in which brokers registered with the LSE can do trades.  it's very affordable and has limited due diligence process.

CSE - This is a Canadian fully reporting stock exchange (securities commission reporting + audits), but it is affordable and their approval process is reasonably fast.