I Have a Log (Spreadsheet) where I track money being spent from
several accounts. (See Below)

Account # Amount
80311 $25.00
80928 $50.00
80937 $75.00
80311 $100.00

I also have a budget. (See Below) *Note* Same Account #'s
Account # Budgeted
80311 $1000.00
80928 $1000.00
80937 $1000.00

One way is to put this in Sheet2!C2 and copy down:
=$B2-SUMIF(Sheet1!A:A,$A2,Sheet1!B:B)

This assumes that each account appears once in Sheet2, possibly several
times in Sheet1, and you want the money being spent to be accumulated on
Sheet2.