I think you're creating unnecessary complexities.
The only case that this really would violate anything is if someone did a 2-for-1 trade, giving them 22 players and $260 cap. Otherwise, they could always get some player for $1 and have a legal roster and legal cap.
Just announce that, if you make a trade, you have to have at least $1 free for every empty spot on your roster. And then let people sort it out. The solution of running the FAAB every night is worse than the problem it's trying to solve.
0-3 to 4-3. Worst choke in the history of baseball. Enough said.