I bought one from B & Q just before Xmas. It was one of the long (5 ') ladder types. It cost me € 135 as there was a sale on towel rails, 1/3 off.
They are easy to install. Just treat them like a replacement radiator. Bear in mind that they need to be balanced like a normal radiator, therefore record the number of turns you made on the original radiator, and adjust the new towel rail lock shield valve accordingly.
Also, towel rails are normally narrower than radiators, and there will be a gap between the original valves and the new valves. You have a choice of either 1) taking up the floorboards and rerunning the original pipe to new location (iggish job); or 2) extend the pipework above the floorboards (easy job but does not look very well - appearance is greatly improved by using chrome/steel pipes and fittings, rather than the usual copper pipes)