Besides factors already mentioned, the fields you're dealing with and the clients you work for affect your pay by a lot.

Financial industry often tends to pay among the most, as a field and as a client (though there's no natural connection between finance and Perl).

So, having some knowledge on certain subject matters matter. If you're talking to, say, some HR lady, and if you understand with ease the HR and business jargons she's talking about, you make better impression.

Many 3, 4-person teams/companies (Perl or otherwise) make anywhere between couple thousand dollars a project to tens of thousands (2 - 6 months of work). You only make millions a project if you're Pixar or really well-connected.