I do think some of the PP cakes are over priced, but others, not so much, although you're obviously still paying for the name. I'm assuming you're not a business though Seeker if you are charging £300 as your maximum price?
You're right Gerrof, the ingredients are expensive, but it's also the time taken. A 'basic' wedding cake will take about 15 hours from start to finish, so even if you're charging £10 an hour for your time, that's £150 before even taking the ingredients, equipment, insurance etc into account. Realistic looking flowers, such as large wired roses can take up to an hour each too, so if realistic sugar flowers are wanted then that can really push the price up.
Most people are happy with 'average' sugar flowers though, there aren't many people left in the UK who can truly make realistic looking sugar flowers. Peggy Porschen is one of them, but personally I think Alan Dunn's work knocks spots of hers, although it's not such a 'romantic' style and AFAIK he mainly teaches these days, I'm not sure if he makes cakes at all any more.
Off to look at the Christopher Garrens website now...