I bid £5 for the gorgeous Willow!
She looks bouffed to perfection there
To work out how much stuff costs to post have a look at this chart - if it's from 0.5cm up to 2.5cm (approx as thick as a DVD wrapped in a jiffy bag) it's a large letter, if it's thicker than 2.5cm it's a packet...
I've worked out my auction stuff already and am knocking a bit off the postage that the bidder pays (auctioneers kindly pay to post the stuff they have donated out of their own pocket and then the bidder pays postage too which is an extra bonus to the amount raised) to try and encourage bidding - as an example who wants to pay £2.70 postage for some ping pong balls (very light, comes in the 0g-750g bracket, but thicker than a DVD so would cost £2.70 to post). By reducing the postage 'paid' by the bidder it will hopefully encourage more bids
As for a start price, again this is just my personal opinion, but if something is likely to get lots of bids then starting it off at 1p or 99p won't hurt but if something is a bit more specialist eg a microchip cat flap (I believe we have one donated by SureFlap again this year), that might only get one or two people bidding on it so best to start the price off at a realistic level so it doesn't end up going for 99p!