Don't forget the hard-water variable. I used DR Harris for a long time on city water, then moved to well water and found it significantly harder to lather.
Adding a dollop of Kiss My Face will make any soap lather better; it was hard for me to find in Canada but now that I'm stateside I see it everywhere.
Tabac is another well-regarded soap that is cheap and easy to get in some regions but not others. (Never seen it myself, and I have plenty of other soaps to try...)
The only soap I've ordered sight-unseen without sampling is ToOBS, and it lived up to the reputation; I wish I could go someplace and smell them all, but I haven't been disappointed by what I've got. It's ridiculously cheap on Amazon now compared to what it used to be, not sure how the cost-per-shave works out.
After 15 years of wet shaving, I haven't found any dramatic changes in performance--even the oft-denigrated Williams Mug Soap works for me once I develop a routine to get some lather. (adding KMF or glycerin depending on hardness of water etc.) So I'd say if you're going for dollar-per-shave you're best off picking up something like a bulk Arko or Palmolive order (should be ridiculously cheap) and figuring out how to get the shave you want with it.
What I have noticed is that I don't buy EDTs/cologne anymore; I usually have some product or other around (either soap or aftershave) that has a nice scent. That's the real value in shave soap for me; I get to try a new scent every time I run out of something.
I'm currently writing a shaving product round-up for a big consumer-reviews site, I'll post a link if I come up with anything interesting re: concentration/longevity of the product I test. (Not testing any pucks, but I sneaked in some popular wetshaving creams.)