One of my local fish stores sells bettas for $2.50 but trust me, you don't want to but them from there. Another sells them for $2.99 which is that same price as Petsmart and Petco. And good ol' not so good Wallie World sells them for $3.50 which in my opinion is insane!! Hope that helped you out.
Never buy from waly world There bettas suck (up hear all of them are silverish with a tinge of purple on the fin tips ugh ) I would be willing to pay more for a good betta and you need to be willing to pay more if you wand a betta with an abnormal tail like a crown tail or doube tail or a half moon tail (this is the coolest one)