When it's a product I've not bought before I always have a good look around on the 'net, but also speak to other people I know in the trade and get an idea of what I should be paying, and when I go into a place to request a price I always make a point of telling them that I've been looking around at prices, not that that makes difference half the time.
I have noticed on a couple of occasions being in varying builders merchants and talking to a general bod they don't really care whether you buy it or not, but a couple of times an area manager/rep/sales manger etc has been present, and what a difference, they will basically bend over backwards to match and/or beat any price to ensure they get your business, that is the difference, put all the sales people on commission and then see how badly they want your business.
Sorry to go on a tangent, but does anyone else notice the lack of customer services generally in many merchants? I am lucky and use two in particular that are excellent, and I have worked hard to build up a good relationship with them, and I feel I get outstanding service even though I am a small one man band outfit that will never realistically break their sales records, but some merchants make you feel like you should thank them for allowing you inside their building, having a chat with their mate for 10 mins whilst you stand at the counter in your Harry Potter invisibility cloak…
Anyway, sorry for the rant, back to the OP, Ridgeons have never been particularly competitive on price, you should be paying half what they've quoted you, but as someone else suggested, look at the narrower board, it should work out a lot cheaper, wider boards are more expensive as a rule.