I bought myself a medium sized chest freezer this year and would strongly advise that you look up customer reviews on any model you may be going to buy before making a decision - particularly if you are wanting a 'cheap and cheerful' solution.
For instance, the Norwest chest freezer will come up frequently, it's not too large and not expensive. But if you check the customer reviews you will find it nearly always has a problem with the lid shutting (a friend of mine bought one and hers does too); a few people have checked how much food it can freeze and found it does not freeze as much as quickly as its literature would suggest, and several have found that it doesn't readily maintain the required -18 deg C internally (whether this is linked to the faulty lid shutting I don't know.)
Even if you are buying second hand you should still be able to find customer reviews on the model itself (try websites like Comet, Currys, John Lewis etc, or just google it) before you decide.
Best of luck!
Cheers
Sally x