What do I need to creat a specific type of game...?

Okay, as a side project to keep me distracted and give me some reason to come home and NOT sleep I'm going to create a game; or atleast attempt. Always wanted to, and have the patience. I want to make another Pokemon game, most likely as a little bull-crap thing for my friends and I. What would be the best program to do this on? Preferably something either cheap or free, but anything recommended is acceptable.