How to use in-app payment without Google Play?
I don't think that Google billing is possible without the Google apps installed. However there are some apps that offer in-app purchase emulation. In most cases they work and in addition you don't have to pay. Lucky Patcher is an app which does in-app billing emulations. However if you are not rooted you need to rebuild the APK in which you want to use emulations and reinstall it.