Full corner weighting is probably not necessary on a road car (and nobody carries ballast in a road car anyway - it's done through changing ride heights on the corners). However, getting it approximately right will make a big difference. Of course, if you sometimes carry a passenger, and sometimes don't, you'll have to compromise one of them completely (or both of them to some extent).
Anyway, properly done, full alignment check of all 4 wheels, following by shimming the rear to align the wheels and then a reset of camber, caster and toe could take 4 hours. But I suspect that you'd get close enough in a road car in an hour. So it should probably cost about £50-£60 in labour.
Jez