How much would you charge for this?

There isn't enough info, here, and you know that. What do you mean by a "custom look"? What kind of hosting is the guy on? Is it already set up? How much learning did you do? How much will you need to do? What do you mean by "basic" content? Have you hashed out a full scope? Did you write everything down? Were you charging for that consultation?

You do realize that the ability for visitors to purchase things through the site is going to cost your investor more than 30 bucks a month on top of hosting fees, unless the guy has a dedicated server and, of course, a business bank account? He's also probably going to need a maintenance contract or some kind of training.

Out of the gate you could ask for 500 to 2k as a very low bid, IMO. I charge 435 just to evaluate, install a few SEO tools, and do a week-long ad campaign, also telling my investors that I will charge additionally for extra hours, if need be, after requesting their express written consent. The whole package I offer takes 15-20. So, it's 15-25 dollars an hour or so. I don't think I've ever asked less than 800 to set a site up, and I was usually very disappointed with the contracts that paid 800. More research, learning, customization, etc. than it was worth for stingy and demanding investors who wouldn't sign maintenance contracts. Can't even put your name on the bottom of their sites.

If you really have no idea, though, why even bother estimating? Putting a price tag on a site is something you do after having gone through the process twenty or thirty times. Follow my advice, here. Just ask yourself these questions:

1) Are you dedicated enough to get this site done in a timely fashion? Say, within a month?
2) Are you able enough to do the work? This might mean abandoning custom features from time to time--so-called empty wells--for the sake of your investors. It also may mean working more hours than anticipated on specific tasks.
3) Is your investor willing and very comfortable with accepting a ranged estimate that is 2 to 5 times as much as you anticipate the workload after having done all of the research required to understand how long the project should actually take you?

If you answered yes to all three of these, give your investor an estimate on hours, give him a contract, tell your investor what you charge per hour, tell your investor that you may need to work additional hours, tell your investor about cart and hosting expenses, offer your investor a maintenance contract and training, and be prepared to justify every single hour you put into building your investor's site.