Lori,
What part of the country are you in, what kind of photography are you doing, what is your experience level, and what is your overhead profile? (Is photography to be your only source of income; do you work from home; have you been doing this for a while or just getting started?)
These factors have more to do with what you charge than what somebody else is charging online.
For example, I shoot sports and corporate events. The same 4x6 I sell for $3.50 to $5 to soccer parents goes for $10 at a corporate event, and $20 if I have to bring out my portable studio and shoot executive head shots. I provide a low resolution (640px on the long side) download suitable for Facebook/Web/etc. for only $0.69 and sell a ton of those to kids on their iPhones. But I also sell medium resolution print grade downloads for 5x the price of a 4x6 for personal use, or 5x the price (that's price, not cost) of an 8x10 for unlimited commercial use. I only upload medium resolution files to Zenfolio. Full resolution files are quoted based on intended use and are never less than $100. But this works for me - your market will certainly be different. I live in Texas but work nationally by the way.
The trick is to provide obvious visual value, and then price sensibly. I see one person responded that they charge 200% of cost. That may be all the market will bear for whatever type of photography they are doing. My "basic" formula is $2 to push the button, plus 500% of cost as a MINIMUM. So, a 4x6 for me would be $2+5x$0.29 or $3.45 which I round up to $3.50. This is a VERY competitive price for sports photography. I adjust up based on the market - charging more for a national championship vs. a weekend match or regional competition for instance.
I shoot typically 2,000 images per day (up to 10,000 images if I have 5 shooters working). Approximately 10% sell. $2+4x.29=$3.16 gross profit per 4x6, less Zenfolio's cut, is about $2.75 net per photo = about $550 profit per shooting day before depreciation on the equipment, etc. Now - how much of that do I need to do to make a living? Or, am I just trying to have a profitable hobby? Or, is this a second income? All of these questions factor into your prices and none of that makes any difference unless you are banging home the money shots. By the way, of the 2,000 images I shoot, at least 500 are money shots - but only 200 will sell at sports events.
When you think about overhead, remember that digitial is NOT free. My Canon 1D MkIII is about $4,400 street with a rated shutter life of 300,000 activations. Now, I will trade up long before I wear it out but let's assume I go to end of life. $4,400/300,000 = $0.014667 or a minimum of $0.015 every time I push that button once or $0.15 every time I fire off a 1 second burst at 10 frames a second. So, from the $550 profit for the day, I deduct $30 for wear and tear on the body (the camera's, not mine), and then start adding in lenses, equipment insurance (you DO have your equipment insured for not only theft but all other risks I hope), memory cards, etc. etc. etc. and pretty soon I am down to around $400 net for the day.
So, lots to think about before you decide how much YOU are going to charge. I highly recommend membership in the Professional Photographers of America. They have great articles on the business of photography as well as a professional service to help you set up your business if this is going to be a full time source of income for you. Their Web site is http://www.ppa.com
Good luck!
Chris