How to calculate budget for web hosting business?

How can we calculate a budget for starting a web hosting business in an economical way? Beginers in this field may think that charges for reseller account or dedicated server is the major part of total expense. But it is a misconcept only. We can hire a dedicated server even at just Rs.5000 per month. But just setup a dedicated server or signed up for a reseller hosting is only small part of our effort. We have to maintain servers in good way. Good way here I means, includes installation and maintenance of firewalls both in physical and software way, 24hr monitoring, instant updation or patching whenever a bug identify etc.