TI-89 Basic - 53 * 0.8 = 42.4

Input y:Input x:Disp ln((e^y)^ln((e^100^-1)^ln(e^x)))

Works by inputting the two numbers, then using the logarithm properties to compute x * y / 100.

If I can assume input from placement in global variables x and y, then this is much shorter, for a score of 32 * 0.8 = 25.6:

ln((e^y)^ln((e^100^-1)^ln(e^x)))

But if it needs to be wrapped in a function, then this works (53 chars again, for 42.4):

:f(x,y):Func:ln((e^y)^ln((e^100^-1)^ln(e^x))):EndFunc

TI-89 Basic - 39 * 0.8 = 31.2

Input y:Input x:Disp ln(((e^y)^.01)^x))

Works by inputting the two numbers, then using the logarithm properties to compute x * y / 100.

If I can assume input from placement in global variables x and y, then this is much shorter, for a score of 17 * 0.8 = 13.6:

ln(((e^y)^.01)^x)

Without bonus (12):

ln((e^.2)^x)

But if it needs to be wrapped in a function, then this works (38 chars, for 30.4):

:f(x,y):Func:ln(((e^y)^.01)^x):EndFunc