I have 60 dollars to spend on a game. Any suggestions for (coop optional, it's cool if they are) fuck-around sandbox type games?

Really what I want is just something I can easily jump into, maybe with my dad and we can just build what the hell ever and have fun with it, Garry's Mod is fun, but it's too high maintenance for a 'simple minded' person like me. I adore space engineers, but I want to try something else, so... any good suggestions for sandbox games that don't require too much thinking? I love space and the ocean, if that helps :P