As others have said, running mixing non-Production and Production on the same server is a bad idea.

One of the main issues is Governance. It is established good practice to separate Production and non-Production to separate environments, so much so that any mixing of environments is seen as bad governance by almost everyone with the skills to work out what you have done or gets to hear about it. With the trivial per-instance cost today of running a separate virtualised non-Production environment, no-one can justify mixing non-Production and Production on the same server instance.

If your customers get to hear you are doing this, you will suffer reputational damage. Period. Potential customers will walk rather than sign with people that take governance this lightly. If you are under statutory regulation than do not expect the regulators to treat this lightly.

The next issue is stability and performance of your Production environment. This will suffer if you mix non-Production and Production on the same instance. If you ever get a Production outage that is caused by a non-Production system do not expect your senior management to treat this lightly. If this affects your stock market price do not expect yuor shareholders to treat this as competant management of their resources.

Part of choosing your own software vendors is to pick one who make either no or a nominal charge for non-Production environments. Vendors understand the need for good governance, and typically will prefer that you protect the Production environment rather than risk bad publicity because you can blame tham that your Production failure was mandated by their licensing policies. If you are talking with a vendor that insists on charging the same for non-Production as Production, this should be your turn to walk and find someone else.

You may want to look at http://sqlserverfinebuild.codeplex.com/wikipage?title=SQL%20Server%20Administration for more details.