Minimum required specs of a Mac for iOS App development

I'm planing to develop an app with React Native for Android and iOS. I need to buy a Mac to run Xcode for iOS app development. I do not have a high budget, which is why I would prefer to buy a (used) Mac with the minimum required specifications that is able to run the latest version of Xcode and iPhone simulator. The app I want to develop is mostly running in the background, so there will be no heavy graphics or computations. I know this has been asked before, but it's been a few years since then, that's why I ask again. I'm happy about any comments about RAM, Processor, manufacturing year or anything else. Edit (November 2019): Just wanted to give future visitors an update: I spent a few hours to test macinacloud, however since it felt pretty slow and a bit overcomplicated, in the end I decided to get a used Mac Mini from late 2014 with 8 GB RAM. In general I am very happy with it, everything works fine (not super fast, but not too slow either). Sometimes I am hitting the limits (for example when running an iOS simulator and having too many other programs running at the same time), however I am always able to just close the ones I am not using right now and get everything to run fluently again. Thanks for the advice everyone, I hope this can help some other iOS-developement-beginners :)