That's ~$40k/year for 100 devs, plus the infrastructure costs. A Jenkins license is $0 (or $100k+ for enterprise support). If it was my budget, I'd have a hard time fronting up a large fraction of a developer's salary to a third party to provide a fuzzy level of support, versus spending zero money and putting the support burden on an in-house team I can trust and directly influence.
TeamCity has great support, I trust them from JetBrains's great work with IDEs, and their top-shelf license is ~$22k (one-off with 1-year of support & upgrade; iirc the yearly support fee is discounted 50% of original license).
Right now we're evaluating GitLab CI and it looks like the way forward (for us).
I appreciate that there's the option, but I'm thinking more along the lines of what Sentry offers: Open source, self-hostable for free, optional paid enterprise support, optional paid hosting for teams of all sizes. In my book that's the perfect lineup.
Travis doesn't offer self-hosting, Jenkins doesn't offer (non-enteprise) paid hosting.