Sorry. It was a trick title. There is no low cost way of building a personal brand.
For a personal brand to flourish, the marketplace needs proof. Proof comes in the form of accomplishments and thought leadership to begin with.
The wrong way to TRY to build a personal brand is to try to build it on weak proof.
The better way is to work on accumulating proof in the form of accomplishments and thought leadership to start with.
For one, it just costs more to build a personal brand on weak proof (if at all you can build one).