A $10 DO box should run GitLab fine for a couple of people. Many of the speed concerns are about GitLab.com which are not due to ruby but the file server (we just moved to SSD and are working on decentralized storage). To make GitLab faster we're using Go were it makes sense, see the part about workhorse in the release announcement. We're very happy with using Ruby and Rails for the complex business logic. It allows us to ship many new features every month.

We had CI as a separate application but it ended up being better to integrate it.