Best site for cell phone batteries?

My (non-smart phone) is in need of a new battery, I think. The phone does not seem to hold the charge any longer. I am told that it costs more to get a battery from AT&T than it does to buy a new phone, I wonder if there is a site where I can buy one for this phone. I don't need all the great stuff from a fancy phone and I am on my family's 'friends and family' plan. I don't want to bother them with this. AT&T store tells me I have to get them involved to get a new battery. Phooey!

LG Xpression2 (C410). Any ideas would be a great help.
Thanks,
PR