The people on the front lines are the ones who are most likely consuming the cash, so to speak, whether that be directly or indirectly.
As an example, if your engineers have the ability to just fire up a new server on Rackspace at will, that means they have the ability to affect your bottom line.
Instead of making this an issue that could possibly cause panic; instead, provide encouragement to your team to keep an eye on these costs. Start by doing an audit of all of the current costs on your team and then ask your team to find any waste.
Afterwards, consider putting some incentives in place to have your team hit the goal of operating under a certain budget, and then empower them to make the decisions. Put a bi-weekly audit/review in place where you and the team look at current costs and review ideas.
As an example, one of your engineers might do some shopping around and find someone cheaper than Rackspace, which would save money. Combine that with eliminating general waste, and you could quickly find yourself operating within budget.
In short, there is nothing wrong with getting your team to participate; it could actually create more of a sense of ownership and teamwork to have people participating in these kinds of decisions.