the only problem with backing someone to finish top 5 top 10 etc is sometimes there are alot of ties so 9 players could finsh at say -5 or better then your player comes 10th at -4 but with 4 other players and then you get something like 1/4 of the odds which is pretty annoying , but on the other side your player can be say 20th at the start of the last round so if you backed him to win he has zero chance , but if he has a nice last round he can still come in the top 10 and you get paid
if it was me doing your bet id have $10 on a top 10 finish and maybe $2 on him to win , just to make it even nicer if he does come 1st!