I've just replaced the radiators in my house, 9 in all. Because all the rads were old ones I had to use tail extenders on them all but not only that the old wall brackets did not go anywhere near the hangers on the new rads so they had to replaced as well which meant making the wall good where the old brackets were and then drilling and plugging the wall to fit the new brackets. Put the cost of the rads on top of that, all were well over a hundred pounds, then £300 per radiator doesn't sound too bad.