Which PPC campaign gives the most for your money depends on several factors:
1. What keywords are you targeting and the price per click? Try to look for more focused keywords or phrases that may not be in high demand, yet yield better results.
2. Your budget - how much can you afford to spend? Many people can rack up a huge bill if they don't place limits on clicks. I once ran a campaign that was showing great results. I was earning a 60% return on the cost of my campaign. The PPC account I was using sent me an email telling me that if I increased my daily budget I could get more traffic.
So, I doubled my daily budget thinking I'd still earn 60%. However, I soon found out that though my clicks increased my sales did not, which means I was spending more for less results.
3. Test - one thing nice about PPC's is that you can test several ideas or landing pages. One of the things many people fail to do is the two-step method. Many people try to sell on the first click. What's better to do is capture their information such as name, email, etc. Provide something of value for FREE and then have them fill out a form to get more information. Now you can follow-up over & over again to make the sale.
To participate in PPC campaigns you need to have a starting budget inorder to get the ball rolling, just like with advertising in the newspaper or anywhere else your going to have to do it for at least 7 times before your noticed. I have this question asked all the time from my clients.
The rest of the advice here is all applicable but I'll chime in my experience...or more accurately my sons.
He was spending between $10 to $12k per month on PPC. He asked me to look at it and offer suggestions. About 30% of his orders come from new customers. That's important because there's no cost involved in the orders from the 70% that become regular customers.
I suggested he there would probably be a momentum effect involved in the advertising and to test it he should turn off all advertising for 30 days. The orders dropped off by 3%, and the NP fell by $1,200.
This meant he was netting an additional $8,800 to $10,800 a month. I then got him to extend it to 60 days off, and 90 days off. The second month the sales fell by 5% and the NP accordingly. In the end, we decided that he'd advertise for 4 months, turn it off for 2, on for another 4, and off for 2 again. Right off the top it added almost $50k to his bottom line without any significant loss of business.
If your advertising is effective you should be able to be high enough in the natural search after a year that you should be able to spend a lot less on PPC.
I'm not sure how the whole search and PPC works but I'm suspicious. The website I put up for my company is nearly a clone of my sons. While he's totally internet, it's just a small part of my company's busines. To establish the site I budgeted $4k/month to PPC. For a year, you'd have been hard pressed to find me in the top 500 or more. About 4 months ago, I cut the budget down to about $500/ on just a couple of ads...all of a sudden, I come up anywhere from 1 to 4 in a natural search. Given what's happened I can't help but think that somehow the alogrithms were keeping me down in the natural to get me to spend more for PPC to be number 1 to 3...and when I quit spending, I just went into the natural search naturally so to speak. I'm no SEO expert so you can take it for what it's worth but that has been my experience. Hope this helps...