I'm intrigued that this might be a way to get some small projects done I've been putting off done (like a simple shopping cart app with a few specific functions, that I just can't get interested in.)
I think I need to find another trade.
$200 a week can definitely get you a shopping cart. But so can $10. And I am not sure how well it will work.
Usually for that kind of money you'd get someone customizing or re-branding an off-the-shelf open source one or some programmer trying his hand out at writing it from scratch. Use of open source components is fine and probably the way to go but its not ethical if you don't tell your client that you're doing so otherwise use a framework.
I'd say something like $500 should get you a shopping cart with the regular functionality. Probably $200 for customizing an existing off-the-shelf one.
Of course these are just my opinions and experience, so they might be completely off target.
If you work 8 hours per day, 5 days peer week, and 4 weeks per month, then you can make $5 * 8 * 5 * 4 = $800 per month. This is 4 times the minimum wage in Romania and Bulgaria -- it is more than enough.