Hello and welcome to geocaching! Prefer yourself for long, cold, frustrating days!
I use the Garmin GPS60 which I can vouch for being a cracking bit of kit. But at £90 or so, I realise it may be out of your price range, so worth checking out the Garmin Extrex as others have mentioned. Just had a look for you and it's £40 on Tesco: http://direct.tesco.com/q/R.200-8029.aspx
When I started out I only had an OS Explorer map which allowed me to get a rough idea of where the caches were. It's possible to do but it was a bit hit and miss!
Worth having a look at the Ordnance Survey's free Get-A-Map website which allows you to downloads maps at every different scale. That'll save you £7.99 a pop or a trip to your local library.
Here's the link for Get-A-Map: http://www.ordnancesurvey.co.uk/oswebsite/getamap/
If you're caching in Kent, give me a shout and I'll do my best to help!