TJ Hughes are offering a binatone satnav for £50 or £45 with voucher from daily paper - bank holiday special.

Not sure how good the binatone is but perhaps worth £45 for a basic jobbie?

http://www.tjhughes.co.uk/pws/ProductDetails.ice?ProductID=8293&redirect=true

If it's a windows-ce based device, which it probably is, you can hack it and install tomtom on it... I have bought a couple of old Route66Mini off ebay for a tenner a time and installed tomtom 7 on them... turns them into effectively a tomtom go

Alternatively there are the Win CE based ones on eBay (from Hong Kong) (Navon N470?)
which run iGo Amigo out of the box. Usually go for about 30 quid posted.

Got this when it was on offer for £47, its now unto £60, maps are ok, however it runs windows in the background, so it can be hacked to run TomTom

http://www.tjhughes.co.uk/pws/ProductDetails.ice?ProductID=4205&cm_mmc=hitsearch-_-google-_-basefeed-_-4205