Albino are the rarest betta form. They are blind and fragile and very few and far between.
In my few years in the hobby I've seen one, emphasis on one, albino. She was sold for at least $1000 if not more. I believe there's only been a handful that have been recorded (I'd say less than 20 out of probably millions of bettas produced each year and the probably billions produced over the last century).
Who am I? Well I am a Junior Member of the International Betta Congress and a breeder of white HMPKs, red dragon HMPKs, black/red dragon HMPKs, metallic multi HMPKs, blue masked HMPKs, and now multi color HMs. Soon to add black HMs. I will be showing in New Breeder class in fall of 2012.