The raw probabilities for passing the Magic Trap (assuming no dice control such as HW and no deliberate path selection):
20 : 50 : 122
or roughly 2 : 5 : 12
That is, one expects to collect from the trap approx. 10.4% per pass, and we can expect 6 passes paying into the trap for each pass collecting from it.
Dice control seems quite important. Although it is also possible to keep the cash low, thanks to "invest anywhere" rule and round gain.