I find the Potato Days very useful, you can buy 1 tuber or 150 and last year they were 17p each or £1.50 per 10, (including a mix of varieties).
I am off to the Hampshire Potato days at Whitchurch this weekend for my mix of several varieties.
You can also get other stuff there, runner bean and pea seeds, onion and shallot sets, organic plants, seed swaps and other goodies. I bought my copper trowel and hoes from Implementations there one year.
Here’s a link that covers a large area of the Country: http://www.potatoday.org/potatodays.htm
