The first line of this news story says:
Call it space grave robbery for a cause: imagine scavenging defunct communication satellites for their valuable parts and recycling them to build brand new ones for cheap.
I’ve heard people use that “for cheap” construction before, but thought it was dialectal (mid-to-northern English). I was surprised to see it in an NZ publication.
Why does that almost pass grammatical muster, whereas “for expensive” (for example) really stinks?
From Google Books…
As @bib says, for cheap may well be patterned after for free, where there’s also disagreement over “acceptable” usage. For me personally, for cheap doesn’t “pass grammatical muster”, but I have no problem with people using adjectival cheap instead of adverbial cheaply.