I highly advise not
to charge per week.
If there is one thing I have found in development is that people don't realize how much they want up front. Usually "it's just a small site, few updates," next thing you know, you are writing Stored procedures to look through their records, keep inventory and so on.
I am not saying this in a way that is bad, in fact I love doing things like that. But I have learned from my mistakes. And charging this way ends up screwing you over.
Think about it, it is a store website. Likely when they see what you can do, they are going to ask for more, and then some more. Maybe an inventory system, maybe online ordering. I would say 80% of the time, my customers add on to their original requests, and most of the time the original
request ends up being less than half of the end product.
Do yourself a favor and charge hourly or price out features. Otherwise you are going to end up paying for your mistake with your hard work and underpaid time. Web coding is a skill, don't get undercut for it.
(I say minimum of $25/hour, and that is for html/css/js only)
Please don't give me the opportunity to say 'I told you so' in a few months