Soapwort (Saponaria officinalis)
$5 per plant in 9cm pot
Soapwort is an old school herb where it’s roots and leaves were made into a gentle soap and used to wash tapestries. You can use it too, read here for my personal experience with it. Unless you are going to be using soapwort regularly it pays to grow soapwort contained as it can be pretty invasive. I know of people whom keep it in a pot near there outdoor tap and wash their hands with a couple of leaves and water before going indoors after gardening.
The smell of its flowers are beautiful. Tis a perennial which is said to die back in winter but mine just keeps on trucking, I do give it a jolly good haircut though. Prefers damp soil and full sun.