I have found a breeder who sells the blue dumbos for 35 each.
Yes it is expensive pet store will sell fancy for around $7, I started my stock with a few different colors bought from Petco (not ideal but at the time I did not know anyone breeding rats), later on the Dumbo gene came from a friend.

Could you explain the genetics of dumbo and hooded as well? I understand the coloring but how would I make a beige hooded dumbo if I originally buy a Beige "self"
Not sure about the genetics of hooded rats I know they are present in every colors, they are what is called marked rats which includes hooded, cape etc

Dumbo and Blue are both recessive which mean to produce a blue or a dumbo both parents need to carry the gene for that trait. In the case of Blue Dumbo it's a double recessive so both parents need to carry both genes.

Here are 3 great sources for rats http://www.afrma.org/fancyrm.htm, http://ratguide.com/ and http://www.ratbehavior.org/