Yes.
A support contract can be covered by a lease so long as it is bundled with a product sale (hardware and/or software) and it constitutes no more than approximately one third of the sale.
the potential dollar value impact that the loss of your computer resources would have on your business;
how liberal a computer usage policy a company has (the more freedom users have to 'do what they want', the more difficult and costly a burden it is to maintain security; and some organization's work processes might require such freedom); and
the security 'track record' of software being used by an organization (again, a sacrosanct computer business process might mandate use of an insecure piece of software -or it might not).
Translating these general guidelines into a number can be a daunting task; for most businesses, at least 20% of your overall 'IT' budget should be earmarked for computer security. In some cases, depending on the above criteria, this expenditure could need to run as high as 50%. Deployment of computer security measures in an unplanned, reactive manner (i.e., "waiting to be hacked, then doing something about it while you're under attack") could easily cost a business at least 50-75% of their annual 'IT' budget. These are anecdotal figures, and each business's outlay for unplanned reactive measures will vary.
"Why should I believe that my business is really at risk?"
We welcome you to use a search engine (searching on terms such as "computer break-in", "was hacked", "keystroke logger", etc.) and see the mounting losses caused by computer vandalism occuring daily; or read a SANS newsletter.