Sporting News has a salary cap Fantasy Football league, FREE. The catch is you get something like 14 trades free and it's pay for more trades after that. Someone cheap (looking in the mirror) can play free and with planning make it through the whole season, including bye weeks without extra trades. If someone was close and wanted they could buy more trades to make the push at the end.

No way to monitor or limit trades, so the person who paid more could get more trades.

Keep looking. There were some that offered a league for $100 and it included a trophy for first place. I don't remember the number of players limit.

Anyone considering the Wipe Out / Survivors pool? Everyone starts even and you just pick a team straight up each week. If your team loses you are eliminated. You can only pick each team once. Last one left wins. (usually doesn't make it half way, so you can run two in a season)