Have a look in this month's Coarse Fisherman Lee. There's a review of a load of carp rods including the Ron Thompson ones.
I don't agree totally with Phil in that you often pay for the name, but a £100 rod will generally have better quality fittings than a £50 rod. It really depends on how much you're going to use a rod and how fashion/brand conscious you are. If you're only going fishing once a week and your rod will spend much of its time in the rests, then provided you're happy with the look and feel of it go for whatever feels right to you.
One thing to remember is that cheaper rods often have a softer action than more expensive rods and will be more suited to short/medium (up to 60 yards) range fishing. It's always worth having a waggle of a rod before buying it sodon't just order a rod offt'internet as this often leads to disappointment.