$5 *and* a limit of 300 rolls..? That seems a bit limiting.
Limiting with respect to only raising $1500 for the charity - how does this compare to what we've raised in the past? I concede that the time constraints may limit the number of rolls, but it seems very artificial to put a cap on it.
But mainly limiting with respect to reducing the already small odds that someone will win. The only winner in this (as in life in general) will be the insurance company. Is it the insurance co who are imposing the 300 roll limit?
From an organizational point of view, you could have multiple tables all rolling 6 dice each, but you just know that people would think that the result of one table would somehow affect the result on another...