There's some really cheap pairs for like $5 a fish and if you buy two of the same fish from the same seller (aquabid) they're most likely siblings. I've been thinking about white HMs but I don't plan on joining the IBC until later on.
But for your first spawn it might be worth it to breed them or not. If you lose the spawn that would be terrible :( But either way good luck and if they're free get em ;)
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.