From what you have said it looks like your steering arm bolts had broken, and if you had carried on driving the steering arm would have detached from from the hub (the bit that the wheel is attached to) meaning you would have lost control of the steering. Looks like Westcoast 4x4 fitted non genuine swivel bearings so they replaced them with Koyo/Toyota ones as it only required a few minutes of extra labour. If they used genuine/OEM parts I would say €350 sounds about right and by the sounds of it money well spent.