Where do you propose I buy critical enterprise software instead?
1: Reevaluate which software is "critical" to your enterprise.
2: Use open source when possible.
3: If it truly is "critical" and there's no other alternative that can do what you need, then sure. "Buy" it, I guess. (Actually, rent a license for it, lol.) That may make financial sense if you're using that software to make more money than the software costs. I'm not your supervisor, and I'm not your mommy. You can do what you want.