3500 is the max and that would be for ex major leaguers (Atlantic League). Also included can be incentives. So if you were once getting paid 2K a day, or 50-80K as a free agent in the minors, 3500 isn't considered good at all. I think MTH is accurate, there isn't a big difference in some of the leagues. The oldest players can be found in the Atlantic League, and many of those guys are just career pro players who are too old by ML standards. I am not sure of the exact salaries but I understand they are not even close to milb pay?
Interestingly, people think that you go to play so a scout will notice you, not sure that is all that correct because a ml scouts job is to scout players for ml and found at the milb parks or at the HS, or reading the release list daily. However, if a team has a need, lets say for an A team for a lhp , they will call the leagues and ask for numbers, these numbers if good will get you looks. As one friend told me, sometimes they will just meet you at the local HS to see you throw, or to hit. Your manager and coaches recommendations are important as well.
FWIW, there are leagues that have caps on accepting players who they consider "vets". This would be for former milb/mlb players with a certain number of service years.
Most teams have one day open tryouts, this is how a player with no prior experience possibly can get into any Indy league without any recommendations. However, like anything else most leagues will only take players on recommendation. Those players never drafted are strong recommendations from a college coach or a scout.
To make it and stay in a milb team from an independent league, it is about numbers. You have to put up numbers for any ML team to consider signing you. You have to put up numbers to play or they will release you as well.
Hope that this helps anyone ,like me, who didn't know much about indy ball teams.