Pokémon! [PTU]
Personally, I'd be fine playing in any Pokémon games. PTU is just one of the few rules dedicated to them.
As for hacking the system, it's only as difficult at you want it to be. If you want it to be simple, you just need to decide on a difficulty, a reward, and some events to shake things up. For example, having a DC 5 check to break even in a season, with things like a drought giving penalties, and higher check giving either extra cash, or a buffer for a failed roll.
If someone really wants the farming aspect to play a major roll, you could lift mechanics for resource management board games. Divide the farm into it's various tasks (take care of animals, watch over crops, maintain equipment and buildings), then have the players divide their times between the task. Task that have too little time assigned give little or no results, while the opposite gives greater reward or remove penalties. That would take a lot of work to design, but some people do like to flex their designing muscles.
There's also the option to grab things from other RPG. I've seen HarnManor mentioned a few times as having rules for maintaining a farm.