lawyerWhy?
Not true. Consider the sentence:
However expensive, they still bought it.
"You can use however before an adjective or adverb to emphasize that the degree or extend of something cannot change a situation" (Cobuild)
E.g. However hard she tried, nothing seemed to work
In these cases, no comma is required; actually, you can't use a comma.
*However, hard she tried, nothing seemed to work
Synonyns in this position:
They still bought it, although, it was expensive.
They still bought it, however, it was expensive.