You can't know exactly how many people will be in the final field, but you can observe that the final field is usually ~2x the initial field, (I just made that up, it's a bogus number as far as I know, but there is some number which is not bogus which would inform your decision.)

So once you know the expected final field, you can base your decision on that. It was literally the most you could have known at the time you were forced to decide. Same as putting your opponents on a range and making the best decision based on that range.


Just form your data set into an EV calc and you'll have your answer. Like, if the field is AAA, then I expect to win 1st prize BBB% of the time and 2nd prize CCC% of the time, etc. You multiply the value of each outcome by the chance of that outcome, then you add all those products together, and you have the EV. If the EV of re-buying is greater than the cost of the re-buy, then you print monies by re-buying.