Iceland are usually a good source of cheap freezers and they've got a sale on at the moment. Their cheapest online price is currently �104.99
http://www.icelandappliances.co.uk/products/Pr oductDetail.asp?ProductCode=LEC-UFZ-U1205W-W
but you can usually find ex-display models, in your local store, for considerably less. You can find your local store's phone number, by clicking 'Store Locator' here:
http://www.iceland.co.uk/
Alternatively, there might be a British Heart Foundation Furniture & Electrical shop near to you. My freezer cost me �50 from my local branch.
Chris