Cant really advise on a model but things to consider are
Battery highly likely that this will have come to the end of its useful life and a replacement battery would set you back around the £100 mark. Not really a problem thou if you are going to only use it near the mains.
If you buy from ebay then you want to be extra careful as you have no warrenty. Personally I would buya second hand one or a refurbed from a shop. That way you'll at least have a warrenty for a while.
click here does refurbed and 2nd hand models
It all depend on what sort of a budget you have to play with, I would really advise going for one from a retailer so that you do have some form of recourse should anything pack up in the first few weeks.