Apple Cider Vinegar Thin2Thick Conditioner from PURA D'OR comes in an 8 oz size, offered here under the Standard option (SKU 84070).
My hair feels noticeably thicker after just a few washes, and the apple cider vinegar scent is subtle but pleasant. The 8 oz bottle is lasting me over a month with daily use.
The 8 oz bottle lasted me about six weeks, which is longer than I expected for a conditioner. My hair feels thicker at the roots and less greasy by day two, so I'm not washing as often. The apple cider vinegar scent fades once it dries, which I appreciate.
I've been using this conditioner for a few weeks and my fine hair does feel thicker, though the apple cider vinegar scent takes some getting used to. It rinses clean without weighing my hair down, which is rare for a thickening product. Just wish the 8oz bottle was a bit bigger for the price.