Thanks for all the advice. The planning officer is helpful and when I told him this "standard" price he agreed that I could find photographs of an identical shed and annotate them with metric dimensions and suggested that failing that I get busy with a scale rule and pencil! He says that SHOULD suffice for prior notice (no guarantees until he sees what I come up with).
Anyway, I think I may need to change building kit supplier. Herefordshire is a funny old place, I phoned every local company earlier this year and only 2 could be bothered to give me prices. The one I chose had plenty of local installations, so seemed a good bet. I thought yesterday that given the plans were a lot more than I'd expected (£720!), I'd better double check the price as I got my quote from them in February. I expected maybe a small increase, but they've gone up 25%! Apparently some of the price increase is due to all steel framed buildings needing a "CE mark" from the 1st of July by some new law and every building individually needing a structural engineers calculations (at nearly £1200 in my case). Sounds a bit fishy to me - why on earth do you need individual calculations for a bog standard 60x30x12 metal shed? You'd be doing the same thing over and over and over again.
So, I've let my fingers do the walking and phoned a few of the larger companies outside the area. The CE thing is apparently correct (the companies I spoke to have it now, it doesn't seem to be a big deal to them). I've got two prices, with much better lead times, and guess what? 20% LESS than the local Hereford bunch for exactly the same specification. Elevation and floor plans are a couple of hundred quid if I need them and one company will refund that against the order when that's placed.
It seems that it doesn't always pay to buy local!