How to deal with pricing fields

Hi,

I have a requirement,

Once users enter the product I have to calculate the pricing (using ztables) and I have to display.

When I am doing it through DO_PREPARE_OUTPUT method, the pricing field is updating at BOL level (means it is displaying the calculated value but it is not saving with this value) not at Genil level. I am redefining the do_prepare_output of standard component.

How can I find it is violating the field property or not?

If it is violating the field property displays at genil level how to move further.

Please suggest any BADI, where I can write the logic?

Thanks

Suresh