Adams FB from Dollar Tree and Ross FB from Walmart will weigh around 4 oz per sheet. I've not weighed other brands, they are noticeably heaver when you pick them up. I'm guessing they will be in the 6-8 oz range.
If you remove the paper from DTFB, you will save about 1 oz, per side. The paper will come off of DTFB fairly easily. Ross FB is much more difficult to remove the paper..