calculator update(repost)

I need a small java script fix... [login to view URL] I need a dollar sign added to the price per gallon field I need a coma to be added to the results field to for the thousands place..ie $340,000.00 Also in the dollar sign field I would like the decimal point to be automatically placed for the user...ie if the the users wants to enter $4.50 then the users should only have to type 450, when the users types the "4" the field should look like .4 then when the users types the "5" it should look like .45, then when the user types the "0" it should look like 4.50 Also...the formula for calculating the percentages is incorrect... Right now it's showing a %15, 20%, 25% increase in fuel mileage translates into a %15, %20, %25 increase savings on the price per gallon...this is incorrect. A new formula must be entered to display the correct calculations. The formula will be provided.