I think Duracell Batteries really are the best. We have a couple of bargain shops that sell them - eg 4 AA for �1.99 - you can usually find them at that price in markets too. Morrisons have a buy-one-get-one-free promotion on some sizes at the moment. Hope this helps.
You definitely want to go for rechargeable NI-mh 1800ma batteries which although will cost you about �7 for 4 (frequently advertised on e-bay) they will last 600 times longer than an ordinary battery !!!