Ok, so an idea similar to Props.
How bout a place (like say, behind 4 dragon or some place, where you can deposit money and earn an interest rate on it, like maybe 5% per 5 minutes.
The interest rate could change from 1% to 10% every 15 minutes to make it more amusing
but lets say the interest rate is 5 percent: you take out 1 million and drive to 4dragon, you deposit your money there, 5 minutes later you go to withdraw your money, you will have 1050000, 10 minutes later, 1100000, 15 minutes later, 1150000, etc...
when you go to the checkpoint with the money, it'll say something like: Interest rate now: 4%, next update in 6 minutes... and there will be a "deposit" and "withdraw" option. for example you can deposit 1 million, go back half an hr later and deposit another 500k, etc. then withdraw all (much like the bank prompt)
of course you will have to deposit your own money, and then make it back to the bank with the money you earned, just like props you will get ur cash back if u crash, etc.
p.s. REMOVE THE CAR CANONS UNTIL THEY'RE FIXED PLEASE. floating train segments are annoying as hell....