If you have still got a fair bit to do you may find it cheaper to get hold of a grassland spray such as Pastor if you can. Glyphosate needs a very high application rate for broad leaved weeds compared to grass weeds. You wouldn't have to worry about overspray killing the grass then either.We brought 5 litres from the hardware store in town for treating the docks etc and Ragwort and mix it for use in a pump sprayer. As it's not for commercial use it seems this is allowed. Damned expensive though but we have managed to kill off one bed of Docks which covered about 1/4 acre in one place. Now it's on to the next bit.
Sodium chlorate no longer available as a weedkiller but you can still buy it from garden centres as a 'compost improver'

Sauer,
If the run off of rainwater from your drive isn't going to cause damage elsewhere, why not use salt?. You can get salt for de-icing your paths etc a lot cheaper than Glyphosate products and nothing will grow for a long time in soil that has been sown with salt.
Peter
As i said SALT, it works on cemetery gravel drives. As i have done it for years now ..........