I think Dean Markley is selling the four string sets only and then making Low B's available for sale as singles strings. Here's what juststrings.com has to offer for Alchemy Low B's...quite pricey too:
http://www.juststrings.com/alchemyra...lestrings.html
The best price for the four string sets I've seen is here:
http://www.stringsandbeyond.com/demarajaalba.html
juststrings.com wants $55 dollars for the four string sets!!
As far as my experience with these strings, I also play acoustic guitar and absolutely love the Alchemy GoldPhos strings. So I figured the bass version should be OK when I started hearing that they would be going public soon. I prefer stainless steel roundwounds and these Alchemy strings are not stainless steel. They are basically a nickelplated string with stainless steel underwraps and the Alchemy coating on top (which is gold by the way, with purple silk at the tuners, yuck!). Anyway, they came off of my bass after about 3 days. They were strung on an Jazz Bass, through the body, and if anyone wants 'em, let me know.