Your thought on how much to charge

I'm offering Search Engine Placement as one of my services and I've oulined the different aspects of what I can do for my customers and how I can potentially increase there placement on search engines but I'm having difficulty on how much to charge.

I don't want to over charge (which I'm worried about) and I don't want to under charge. I thought about just telling them I'll do it and charge them later but that could blow up in my face if I charge too much. I was thinking of offering $50 or $100 but I'm not 100% sure on what my customers will think. I'm moving towards offering $100 but when I put myself in their shoes, I kinda think that it way too much.

I can justify offering $100 by saying that the amount of traffic and potential busy will be a pay off but again, I don't know how well that turn out.

What's your opinion on Search Engine Placement?
If you were in my shoes, how much would you offer?

Something for you to think about ---

In most cases, good search engine placement is almost priceless, and is in alot of cases worth more than the actual site itself. If you are positive that you can get clients good search engine placements and have the background to back it up, you can easily add a couple of 0's on that 100 dollars...

I guess I'm worried cause it's a real small site.
I've kinda made up my mind that I'm going to charge $100 for that service for small sites and $??? for larger.

I know exactly what you're saying and that's how I feel to. And the best thing is that I can justify that amount if they question why.

It's the decision of your customer, you should charge whatever you find reasonable. $ 100 is a good price, but if you think it's to much you might consider offering them a discount if they purchase additional services (for instance submission updates after a couple of months).