From Longman Dictionary of Contemporary Englishknockdownknock‧down1 /ˈnɒkdaʊn $ ˈnɑːk-/ adjective [only before noun] informal CHEAPa knockdown price is very cheap
Examples from the Corpus
knockdown• The dot.economy turned out to be just a more expensive way of selling old-economy goods at knockdown prices.knockdownknockdown2 noun [countable] when a boxer falls down when he is hitExamples from the Corpus
knockdown• Roper, who is as sharp with a put-down as he is with a knockdown, has run out of worthy opponents.• Kids getting out of Intro thought they were hot, anxious to get the first Kilroy, or punching knockdown.• The second knockdown came early in round two.• The younger fighter seemed to have recovered from the knockdown.• But there is little doubt that the knockdown had a crucial bearing on the fight. 