Part 1 - Welcome to the Mac Game Store. They even have a weekend sale on Simulators -- which sounded completely boring until I saw Euro Truck Sim 2, Cities: Skylines, Goat Simulator, and I Am Bread. lol
http://www.macgamestore.com/showcase/Simulation-Weekend/
Part 2 - Steam's summer sale will be going on from June 11-20. Pretty much everything on there will be like 66-90% off, so I'd suggest waiting a week on any suggestions you may get here.
Part 3 - Allow me to informally advertise my Steam game store in the TBT Marketplace, too. c;
And finally,
Part 5 4 - The actual helping part.

Are we looking for something else
like Isaac, or are you looking for something completely different?
Further, if you're looking for something like Isaac, is it the rogue-like elements that most appeal to you (the randomized dungeons, randomized pick-ups, perma-death, etc.) or the general dungeon-crawling?