Retargeting is display advertising, aka banner advertising. Usually, display advertising is charged by CPM (cost per thousand).

For a normal banner ad, you might set your budget at around $1 CPM all the way up to $5 on the high side; even higher if it's a premium location.

With retargeting, you're going to pay $3 - $8 cpm. It's a little bit higher, but a much higher quality viewer looking at your ads.

Especially when you factor in this viewer may have already become a lead and may be viewing your ad on a site like USAToday.com.

While the cost may be a bit higher, in the beginning you won't be able to spend a lot of money even if you wanted too. This is because you first need to build up your cookie pool.

If you only have 2,000 people in your cookie pool, and you're paying $5 CPM, you're going to have a hard time even spending $100 in a month. That would mean all 2,000 of your cookied audience would have to see your ad 20 times.

With some of our clients who have been with us a long time we are now seeing cookie pool sizes of a quarter million, half a million, and more.

At $5 CPM for them it's easy to spend $500 per day.

Expect your costs in the beginning to be very minimal and then for the costs to grow as you increase the size of your cookie pool. This is not to be feared either because the ROI on these impressions is often $3 for every $1 spent.

...If you're doing it right.

Which is what we'll talk about now.