For those that love Retayne and Synthropol....have you considered buying it by the gallon? These products were developed for dyers so you can generally find them for less money through these resources/companies rather than smaller quanties from fabric stores.
I have purchased from Colorado Wholesale Dyes by the gallon both Retayne and Synthropol products. (Disclousure: I'm in no way affliated with this company, with my research background I always search for the most inexpensive way to purchase products I like) There may be other companies Colorado Wholesale is the one I've purchased from.
I just called and the current price for a gallon of either product is $19.99. Of course there is shipping to be added, but if you buy the 8oz bottles at your LQS or fabric store they can run anywhere from $6-12 per 8 oz bottle.
Colorado Wholesale Dyes phone number is: 1-800-697-1566. For those living in the Denver metro area they are in Littleton and you can pick it up. My experience is with this company friendly and outstanding customer service.