For underwater divers, according to waterwelders.com:
"According to commercial divers and global statistics, the average underwater welding salary is $53,990 annually and $25.96 per hour. However, most incomes float around $25,000 – $80,000. Diver welders in the top 10% make $83,730 while the bottom 10% pull in $30,700."
For traditional welding, Payscale.com states that it's $17.71 an hour.
All of those numbers though will vary by experience, location, and company!