I know there should be big difference between various countries.
A developer with two years of experience in China may earn 15,000 a month(21.75 days), or 86 RMB (~12.5 USD) an hour (8 hours a day).
The best blockchain developers can't be bought -- and certainly not by the hour.

Best blockchain devs have many bitcoins, like Gavin, he has more than 10000 BTC, why he works for others for normal rates? He doesn't need to work any more and coding is his hobby, maybe he will work as a CTO or co-founder in blockchain startup.
Source? I have never seen Gavin posting his BTC totals? He gave away bitcoins per hour back in the day, with his faucet.

.... In any way,
most Blockchain developers like him are multi-skilled, so they can be employed for any other project too. These guys should consider handing
knowledge down to the second generation of Blockchain developers. { write educational courses and books }

Look at these salaries :
SAP ABAP Developer Salaries
Denken Solutions SAP ABAP Developer $74,730
V.L.S. Systems SAP ABAP Developer $70,873
Wise Men Consultants SAP ABAP Developer $81,874
Accenture SAP ABAP Developer $89,432