A good article here: http://www.triptomyblog.com/business-it-support-services-6-things-you-should-know/
6 simple points but some which are rarely thought about.
24/7? Do you need this? If you do then you really do need it and many companies find this difficult to obtain at reasonable cost. IJNet will analyse your needs and can provide a very competitive quote.
Cost prediction. We have been specialising in SMBs for many years and pride ourselves on cost effective support. Do you really need the latest all singing and dancing system? Cheap desktop machines can be very reliable and, as long as recovery options are in place, can take the place of big iron servers (which would need recovery options in place anyway).