Actual roguelikes give you the best bang for your buck, hundrets of hours of fun for no money.
Here is a modern, streamlined one. Multiple winner of the Roguelike of the Year award. Tales of Maj'Eyal
Here is a not so modern, very straightforward one that is probably pretty close to the original experience. Dungeon Crawl Stone Soup
Here is a complete world generator with the goal to assist you murder your Dwarf Fortress in the most horrible ways once you get bored of it (or without your consent). The game influenced Minecraft and was selected among other games to be featured in the Museum of Modern Art to show the history of video gaming in 2012. Warning: Includes dwarves throwing tantrums if you dont manage to make enough booze for your fort! And don't dig into hot walls or lava will flood everything! I recommend downloading one of the tileset packs from the forum that include the game preconfigued. Dwarf Fortress
Here is a really weird one for when you want to capture little girls in pokeballs to use them as pets, only to then graft bodyparts of other pets on them to give them more item slots
Or you are just a boring wizard and cast spells. Your choice! Game is definitly more on the grindy side. : Elona Plus