[ZeonOne]

One way for low level to catch up is Gymboree Day with a SUPER DONATOR Pack, cost $100 Times (Number of Levels) with an addition of 5000 for every increment of 10 levels.

This Pack give you an addition of 1 energy refresh rate. This Pack + regular donator pack would definitely give the lower player a day to catch up.

As such...

Level 1 - Cost 100 for this pack
Level 5 - Cost 500
Level 9 - Cost 900
Level 10 - Cost 6000 for this pack
Level 15 - Cost 6500
Level 20 - Cost 12000 for this pack
..
Level 50 - Cost 25000 for this packs