Here's what I discovered, since I am unfamiliar with the JAM paper company.
JAM vellum bristol in a 67 pound weight is available on Amazon for $10.99 for 50 sheets of 8.5 x 11.
Canson XL vellum bristol in 100 pound weight is available at Consumer Crafts for $4.76 for 25 sheets.
I would not use a 67 pound bristol for water-based media. It's too lightweight.
In addition, the Canson is cheaper per sheet than the JAM, and it is a heavier weight paper.
Obviously I don't know which JAM paper you are comparing to which Canson paper, but I have found Canson to be a good quality paper for a good price in all of their lines.