I'm confused. If the bids are for a wall like one in your picture, they should have included whatever is necessary to make the wall function -- like a concrete block base that the bricks are built around. Did the bids not include this? Or were the builders just not clear with you about what exactly was involved?

What about limestone?

I'm certain we discussed it...we're also doing a fire pit and I told them I want the cap to be a brick and a half wide, same as the wall. We even discussed the row of filler brick that would be needed for the inside of the pit. I realize the obvious answer is to bite the bullet and pay for them to do a filler brick (if they hadn't actually thought of it, too), but I'm on a tight budget and feel like I'm already paying a premium price for their labor.

We could do limestone, however, since the wall is curved, every single piece would need to be cut and shaped to fit the curve. The only reasonable answer for a cap other than brick would be precast-I've spent a month trying to locate some locally to no avail. I can order them from a place two hrs away and they cost a fortune- almost as much as the four cubes of brick I just ordered!

"I'm confused. If the bids are for a wall like one in your picture, they should have included whatever is necessary to make the wall function -- like a concrete block base that the bricks are built around. Did the bids not include this? Or were the builders just not clear with you about what exactly was involved?"

^^^--- this.
Did the bids not included the cinder block (or whatever)?

What did the bids actually say? Is it possible this is included but your not understanding the nomenclature used?