Cash would not work unless it was really significant amounts.
1st- $500,000
2nd- $450,000
3rd- $400,000
4th- $350,000
5th- $300,000
6th- $50,000
7th- $25,000
A system like that may work, but it makes the difference between the elite and the average teams even bigger. That is not ideal imo.
And as for the playoffs going into a tournament, I disagree. Leave the top four teams to battle it out as is. Just throw all the 6th and 7th place teams into the tournament. As I mentioned the teams that are throwing games, know that they are likely not going to lose in the relegation. A tournament style system also evens the field in some ways. There is a big difference in many leagues between the confrences talent wise. So the best teams don't always win, there are many good teams that have relegated, but are significantly better than alot of teams in the division above them.
My team is a great example. Right now I am 4th, realistically I will finish 4th, 5th or 6th. If I were to throw some games to finish 6th I would face a team that I just beat by 60 points. Not really a big worry about facing relegation, as in all likelyhood I would win it pretty easily.