Budget Table need to get next budget id ans amount

HI

 I Haveing table like Budgetdetails in this table instcode budget id budget amount 

intcde -Inst0001 budget id 01 amount 150000

instcode inst0001 budgetid 02 amount 25000 what i want  one form i enter stock for thids institute when i enter stock that related cose efeetecd in data base that id store if the stock amount is more than first budget means budget amount id 01 150000 next attometicaly need to get second budget id and amount

any body please help