This is on sale for the next 15 hours on Steam for €13,04 inc. the expansion (make sure you don't get the cheaper option without the expansion):
http://store.steampowered.com/app/34611 ... l_Evolved/
It also has PC-Mac crossplay: https://blogjob.com/oneangrygamer/2015/ ... nux-users/
After Rust, I am very interested in these games, and this seems to be the next step up from it because it has a longer/more complex endgame, which is Rust's main issue. We still have some time before we are done with Rust, and I would like to try Astroneer after, but sometime in the next couple of months I'll look into starting a group for this one, and this is certainly the cheapest this game is going to get within that timeframe, so grab it if it looks like something you'll be interested in, and post here so that I have some idea of how many people are interested.
Note also that it supports the Rift, but doesn't require it.