The meaning of a phrase that has one of four-letter words

"I draw dick unless the price is right" in this passage is probably meant to express "I draw nothing unless the price is right" (which would more commonly be expressed with the negation on the auxiliary, as "I don't draw anything unless the price is right"). It's not clear what the word "draw" means without more context, but it doesn't really matter. As Peter Shor says in a comment, the imaginary context of the statement may be "an artist saying he won't work for free" [or for less than his work is worth]. Or, as fixer1234 and aparente001 say, it may be that in this example "I draw" is being used with the meaning "I earn."

The comments beneath your question seem to indicate that this use of profanity is not especially familar to all English speakers. "Dick" can also be extended to "dick all" when used with this meaning.

The passage is about the use of profane words as substitutes for either negative words, such as "nothing" or "nobody," or negative-polarity words, such as "(not)... anything" and "(not)... anybody."

In standard English, usually a single word cannot be used in both of these contexts. (In some varieties of colloquial English, words like "nothing" and "nobody" can be used in both contexts.) The author is pointing out that the synonymy of "I don't draw dick" and "I draw dick" might therefore be seen as unusual.

It also contrasts with the use of "shit," which for many speakers does generally have to be used with a clause-level negation: "you don't know anything" is much more likely to be expressed as "you don't know shit" than as "you know shit" (though the second might be possible for some speakers).