Jug

Jug last sold for 3 gp (instant sell) and was last bought for 4 gp (instant buy) on the Grand Exchange.

You can buy 13,000 Jug every 4 hours. The 4 hours start from your first purchase, and only buying counts towards the limit.

High alchemy turns Jug into 1 gp. Buying one at 4 gp and casting with a nature rune at 138 gp costs 142 gp. That is a loss of 141 gp per cast at the latest prices, so it is not worth alching for profit right now.

It is not on the exempt list, but it pays no tax at its price. Selling one at 4 gp costs no tax. Items selling under 50 gp pay none, because 2% of the price rounds down to 0 gp.

The highest daily guide price on record for Jug is 117 gp, on 28 Mar 2015. The lowest is 1 gp, on 15 Nov 2019.