You do have to remove the rear seats, c-pillar trims & parcel shelf to access the nuts that hold the top mount for the shock. £325 doesn't seem a complete rip-off although I always do my own work so I'm well out of touch with garage prices..... It's difficult to compare the same job on 2 different makes of car & prices will vary accordingly. Ignore anything a main dealer says, they are the biggest rip-off merchants out there! Thing is you should really have both done at the same time as 1), it's good practice & 2), they will have to pull it all out again to do the o/s when that fails!