how to get the difference in value of two columns with reference to another column

Hi,

Hope someone could help me out with my attached spreadsheet. Basically I just need to autopopulate the amounts in column H.

As you can see in columns A-D, i have the details. And in order to get the value for column H, I need to

1. Lookup the account that I need using the acct code.
2. Return in column H the value of that code. The value is the amount in column D less the amount in column C.
3. You may notice that Car Expenses in column H is a combination of accounts 200.00-600.00, so I would also need the formula to be able to identify the codes in between.

Hope this makes sense and hope someone could help me out.

Thank you!.