Normal bottle price is ?4.69 - the ?5 is taken off before the VAT so need to add on an additional 17.5% to the ?5.00 ( well I am an accountant!)
You do have to join - ?20 or ?25 per year (plus VAT) and this can be done through a firm or personally if you are a nurse / police / professional etc. The website
www.costco.co.uk explains the trade membership well but not the personal one for some reason.
They have discount vouchers running on a weekly basis which are sent out in a booklet so you know when some wine is on offer well in advance. Otherwise it does tend to be cheaper.