IT Budget

Get to know what GL's your department has by talking to finance / accounting dept

Also ask them what the depreciation cycle is for CAPEX Purchases

Split your budget in two - CAPX & OPEX

CAPX - Capital Expenditure - the expensive things you get once in a while. New Servers, workstations and so on. In other words - things that you keep and depreciate over X Years

OPEX - Operation Expense - The more day-to-day spending like services including Internet, hosting

Does your budget also include co-workers pay or is this purely an IT Expenditure budget?

Work out total licensing costs - divide by 12

Same for all other services like Internet, copier rentals

I would love to give you more - but with out knowing what you have it is hard.