1) Putting a price in your ad will reduce your ad space by at least 5 characters (e.g. $19.99). So if you're trying to maximize your ad with the best BENEFIT-driven words, a price tag might get in your way.
2) On the other hand, if you're trying to QUALIFY your potential visitor, and only want visitors who are serious about your product, then putting in the price tag MAY weed out some of the "looky loos". If your product is highly priced, it may be worth doing, but if it's a clickbank affiliate product, it's probably not worth it. The best thing to do is to lead your visitor to a landing page that presells them, captures their email address, and then sends them off to the sales page.
I wrote a couple of reports on how to maximize Google campaigns so that you can squeeze more money out of your campaign. If you're interest, just send me an email. My address is found in my User profile.
Huey