The rules aren’t entirely clear about these situations, but here is how I would award the prizes:
Situation 1:
Arnie $200
Alfred $112.51
Bernie $112.51
Alonzo $0
Bob $75
Situation 2:
Arnie $200
Alfred $112.50
Bernie $112.50
Alonzo $0
Bob $75
Situation 3:
Arnie $200
Alfred $112.50
Bernie $112.50
Alonzo $0
Bob $75
As I see it, the three situations are essentially the same. Clearly Arnie gets the undivided first prize of $200. Alfred and Bernie tie for second, so under 32B3 they split the second prize of $150 plus one of the class prizes, but which one?
In Situation 1 Alfred is eligible for the Class A prize and Bernie is eligible for the Class B prize, so either one of them could bring that prize into the prize pool. Rule 32B1 says “A clear winner of more than one cash prize must be awarded the most valuable prize.” Extending that principle, Alfred and Bernie are collectively better off winning $150 + $75.02 (2nd + A) than winning $150 + $75 (2nd + B), so Alfred brings the A prize into the prize pool and Bernie brings the 2nd prize into the prize pool. This leaves only the class B prize of $75, which Bob is eligible for and Alonzo is not, leaving Alonzo with nothing.
Following that same logic, in this perverse prize structure:
Situation 4:
1st prize $200
2nd prize $150
top A $75
top B $75.02
I would award $112.51 each to Alfred and Bernie, $75 to Alonzo and nothing to Bob (assuming someone else designed the prize structure, since I would never design it that way.)
In Situation 2, Alfred and Bernie are both eligible for the U2000 prize and only Bernie is eligible for the U1800. The prizes are the same amount. Rule 32B4 says “A player who is eligible for more than one class prize of an identical amount shall receive the prize for the highest class involved.” Therefore Alfred and Bernie split the 2nd and U2000 prizes, leaving the U1800 prize which Bob is eligible to win and Alonzo is not.
Situation 3 is similar to Situation 1 except that now the Class A and B prizes are the same amount. I would still give Alfred and Bernie the 2nd and Class A prizes, but now I’d do it because of rule 32B4 (“A player who is eligible for more than one class prize of an identical amount shall receive the prize for the highest class involved”) instead of 32B1 (“A clear winner of more than one cash prize must be awarded the most valuable prize.”) This leaves the Class B prize, which Bob can win and Alonzo cannot.