Great question!
While the pilot is an FO in the Accelerated Captain Program, their pay is the same as all of our FOs at $31,000/year. It will take you less than a year to get up to 1,000 TT and become a restricted Captain (right now some of our ACPs are upgrading after just 3 months in the right seat).
When the pilot gets to the restricted Captain portion, they'll get regular 99 pay at $44,000/year. When they become an unrestricted Captain, they'll get regular 99 pay at $44,000/year.
We are currently looking at increasing the pay for the BE99 Captains; nothing set in stone yet, but we see an increase in the near future.
After that, there are defined preferred hour times to get into the BE1900, SA227, and EMB120. With those, of course, come pay raises.
Hopefully that all made sense! Let me know if you have any other questions!