Developer tooling (Developer machines, IDE's, source control, CI, issue tracking, etc): Pay for the best.
The product: Only use FOSS. Give back by contributing and by making some of our work available as FOSS.
For the product, especially for the client-side, I just see it as too risky to include proprietary software. Even if the pricing is fine for right now, it can easily change later (got burned by both Google Maps and Mapbox years ago), and in some cases even prevent you from using different pricing models because of base costs it may add per user.
On the infrastructure side I'm more flexible, but even there: 1. Stick to commoditized services as far as possible, where the pricing is predictable. I'd include most cloud services in this, and most "enterprise" offerings not. 2. Avoid hard vendor lock-in if feasible, but only up to a point (don't build something from scratch just to avoid the lock-in).