It depends on your audience. I've got one group on a forum that I could offer $10 bills for $5 and no one would buy. Most don't have $2 to spare, just looking for free ways to make money onthe net.
Then I have another group which feels like "it's only $5, go for it."
And there is one other group I could probably do the opposite, sell $5 bills for $10 and get some orders.
The correct price is the one you bump your way up to until sales fall off, then come down to the previous price for a year and try again.
A large retailer did a trial about 2 years ago with a group of womens dresses. They offered them at their regular markup at a price of about $ 34.95. Sold fair, but not great.
They dropped them to $ 29.95, but not as a sale item, just everyday $ 29.95. No real change in sales.
They then RAISED the price to $ 39.95 and the things started flying out the door!
Went to $ 42 or $44.95 and sales fell back off.
Over the test period they sold something like 85% at the $ 39.95 price.
So, start fairly low and have incremental increases until income begins to fall off. Keep in mind that 100 at $35 is better than 80 at $40.