Adult Helmet size small

If anyone has a used helmet they are willing to part with cheap I might be interested. Cheap means around $20 plus shipping. I am not expecting much for this price, as long as its a full face and it's ***. I would also expect that the helmet would be usable as in the liner and straps are in tact. This helmet would probably get little use. It's for my dad who seems to have an unusally small head and my 2 helmets(L, XL) wont fit him, thanks
Jason