Tattered hat priced at a very low cost (4,5)
I believe the answer is:
dirt cheap
'at a very low cost' is the definition.
'tattered hat priced' is the wordplay.
'tattered' indicates anagramming the letters.
'hat'+'priced'='hatpriced'
'hatpriced' anagrammed gives 'DIRT-CHEAP'.
(Other definitions for dirt cheap that I've seen before include "for very little money" , "attractive to potential buyer?" , "at an extremely low price" , "next to nothing" , "Inexpensive (as muck?)" .)