As I said in another post, you can get a hosted build server from Visualstudio.com (VSTS) with unlimited Git repos, with 5 users and a hosted build server with 240 minutes per month. You can get a hosted build server with unlimited minutes for $40 a month. If you need more than one simultaneous build - buy more build agents.

VSTS has hosted build servers for Windows, IOS, Linux, and Android.

It's even nicer not to have to maintain servers at all.

I try to avoid maintaining servers. We are moving to serverless functions with Lambda and serverless Docker with AWS Fargate.