What does ‘make a buck off’ mean?

Solution 1:

As stated by drm65, making a buck off something does mean making money off it.

In the example you gave, there were people who were about to

make a buck off fearmongering about the 405.

Having just read a version of the article, there are quite a few businesses mentioned to be cashing in on the situation. (Many of the businesses are using the opportunity to increase business by targeting their advertising, or offering discounts to the many people who have chosen to stay in, rather than travel, during the highway closure.)

With regard to the word buck meaning money (or specifically, a dollar), I think that came from the idiom pass the buck, which originated as poker terminology. This is what The Phrase Finder had to say on the topic:

Players were highly suspicious of cheating or any form of bias and there's considerable folklore depicting gunslingers in shoot-outs based on accusations of dirty dealing. In order to avoid unfairness the deal changed hands during sessions. The person who was next in line to deal would be given a marker. This was often a knife, and knives often had handles made of buck's horn - hence the marker becoming known as a buck. When the dealer's turn was done he 'passed the buck'.

Silver dollars were later used as markers and this is probably the origin of the use of buck as a slang term for dollar.

Solution 2:

You are right.

Buck is a slang word for dollar. So making a buck off of something translates to making money off of it, and it's used here as a metaphor for making profit from it or taking advantage of it.

Solution 3:

Short answer: Yes. OP has guessed the correct meaning.

Long Answer: Make a buck off can be used to mean just make a profit from, with 'neutral' connotations as can also be conveyed by make a buck from, but...

...using the word off rather than from often implies ‘to take advantage of’ (i.e. - the profit will be made at another's expense, rather than a well-deserved reward for good planning, hard work, etc.)

Just my personal opinion, but I also think off is more 'slangy/informal' than from here. Not that it makes much difference, since make is slang for earn (or acquire in less honourable ways), and buck is slang for dollar, so off can hardly lower the tone much more.

LATER: Regardless of other answers, OP's focus in this question is use of the word "off" (not buck). So I'll just say that although the principle isn't universally applied, people are more inclined to use Make money off [exploited customers], as opposed to Make money from [some more morally justifiable enterprise].