Good thread, Aequitas. I'm looking forward to seeing your results. I'm actually more interested in offline-to-online advertising as opposed to PPC. Especially because you have pretty fine grain control over the placement of your ad. That's more true of space ads than classified.
Also, what you said about offline-to-online conversion being higher is true. But that's because the only traffic you're getting to your site is people who are so interested in the offer that they got off their ass, went over to the computer, and went to your site. So what's really happened is that by the time they're at your site, you've already had your first, and biggest conversion.
BTW, the comment telling people not to write a long copy ad is poor advice. The type of ad really depends on what you're selling. Of course, for something low margin like your $35 offer, a classified ad is best. But if the numbers show you could make your money back on a larger ad, especially a space ad, long copy always wins.