How can I find out amount of unallocated budget

How can I find out the amount of unallocated budget funds?

I assume you are asking about the difference between your estimated budget allocations for the year and the amount that has been allocated to specific budget subcategories. You should find this information in the screen where you set up your budget or on the budget report itself.

This is the View/Edit Budget screen. It tells you the difference between allocated and total yearly budget amount (including your estimates of future quarterly allocations).