I don't know about other barks, but I have a market for sassafras root bark. $7/lb and the red/purple in the spring/late fall is preferred...it must have NO wood attached.
I paid $20-22/lb dry last year for goldenseal as long as it was completely clean. I think the tops were at $3/lb clean, green, and dry.
If you have large patches of goldenseal, late summer might be a good boost for you. Be sure to not dig them out, and did the large mature plants (usually about 50% of the patch). I don't have enough wild goldenseal here to dig for weight, but I do dig some wild to transplant into beds. It takes me about an hour or two to fill up a small sack...maybe 200 or so roots. If I were to guess, I'd say that was about five pounds of green roots. I'm sure you will do better farther south as you have a better growing season.