As a general rule the pay for umpires is very uniform. A new umpire and an experienced umpire both working the same game are usually paid the same rate. However, occasionally larger organizations (e.g. a youth league) will pay umpires of different experience at different rates.
As you might expect, umpire pay varies around the country. What an umpire receives working a 12u game in Southern California may be different than what an umpire receives for a 12u game in Maine. Generally youth leagues will pay between $15 and $50 per game, per umpire. High school is typically $50 - $75 per 7 inning game, per umpire. Tournaments are paid at a different rate. Typically a youth umpire can make between $200 and $400 for a weekend’s work. Couple that with weekday work (2 games x 3 nights a week) and a beginning umpire can easily make an extra $500/wk working part-time. Taxes are usually not withheld and the umpire is given a 1099 at the end of the year.
I know a 17 year old umpire in the Midwest who works for a competitive youth softball league. He is dependable, hard-working, and has a great attitude. The league has a 75 minute time limit on their games. This young man works Monday thru Friday, two games a night. he does not work Saturday or Sunday. His pay rate is $25 per game, so he takes home $250 per week for 17.5 hours of work (5:30-9:00). That's an hourly rate of $14.28! Sure beats the $7.50 an hour his buddies are making at the Piggly Wiggly.