Hmm, I'm not a writer so maybe I should abstain from answering.
However, I've read so many writing books that I think I can qualify as "advice giver (amateur class)".
So, my advice is to NOT do it.
From all the books I've read, the idea is to never pay for submissions as the point is for them to pay you.
And at $3 a submission all they need is 15 submissions and they have their text essentially for free, any more than 15 submissions and they're making money.
But please take note of my first sentence...