Spending a fraction of that to monitor that sort of infrastructure is absolutely justified. I can tell you from experience that datadog gives discount even for 100+ hosts, I don't know what they can do for 2500, but if it were me I wouldn't accept anything less than 50% off.
Honestly you need to forgot about your salary, it's irrelevant when it comes to running a company. Imagine a driver in a shipping company deciding to deliver on a scooter rather than a truck because the truck is worth more than his yearly salary.