I'm heading overseas (Central America) in a month's time and I'm looking to buy a (cheap) secondhand laptop as a gift for a charity organisation in Guatemala.

At the moment I'm looking at ex-lease laptops on particularly on TradeMe. However, there are a lot of different companies out there and some of them don't seem to have the best feedback.

Any recommendations for:
-Where to buy good secondhand laptops?
-Recommendations on what to buy? - at the moment I'm looking at maybe a HP Compaq 6930P or possibly a HP Elitebook 2540p, but I'm open to suggestions, just my budget is limited.

I'm not worried about battery issues - it just needs to be able to be plugged in and run off a power supply. Only choosing a laptop because it is easy for me to take with me.

Any help or suggestions would be much appreciated. Thanks!

The charity I'm donating it to is Forma Guatemala (https://www.facebook.com/formaguatemala/) who help with education and scholarships for rural Mayan children. I've had a bit to do with them for several years now so I know that they are geninue group who do make a difference.