Tomble,
If you can't afford to get a big brake kit do the following:
Just stick with nissan discs- they are much cheaper(£60-70) and pads will last so much longer.. aftermarket grooved and drilled discs are imho a waste of money..
Pads make a lot of difference.. Nissan are very good but too expensive(£50+) so try ferrodo or ebc.. expect to pay no more than £40 for a set of ferrodo ds2000's(not entirely sure if i've got the name right
) or around £30 for ebc green stuff..
You can also change your brake fluid and hoses but this really doesn't do much..
I agree with jasegould
i've tried every combination of brake setup and found bigger discs and callipers to be the only answer..
Hope this helps
Sam