I think if you were to release a new book, you should target it at $7-$12, rather than $1.

The hurdle of paying anything at all, is likely to stop many from going any further and on the opposite side, the people who are probably likely to still pay (they read your free book / know your rep) - are probably quite happy to pay a higher price than $1. Therefore limiting your price to $1 would lose you money.

e.g. Free price - 335,000 downloads - $0 sales.

$1 price - 26,000 downloads - $26,000 sales

$7 price - 13,000 downloads - $91,000 sales

- This is ultimately why you would have to experiment with pricing and see the effect on your sales cycle. Often a higher price yields a greater profit, as the number of sales doesn't drop as much as expected.