The guy I use has quoted me £18 for a bush and he tends to use gen/OE parts.
As has been suggested, the price difference is so small that it's a tiny fraction of the labour for when it needs redoing in 12 months time. If your doing them yourself, as Seatown says it's not a quick job and you probably won't want to unecessarily do it twice.
If you intend to keep the car, it's probably worth using genuine/OE quality parts, if it's just a quick fix to get rid to a dealer, it's up to you I suppose.