Probably mostly homemade: It’s a lot easier than you’d think to make the materials for a rocket, especially if you’re not too picky about the details. But there’s almost certainly some professionally-manufactured stuff in there, too: No embargo is ever perfect.
Apparently the cost of a Qassam rocket is about $800, while the cost of an interceptor that is part of Israel’s ‘Iron Dome’ defense is about $50,000 I think. If Hamas can keep launching rockets it would eventually drain Israel’s coffers… although I don’t think that will happen any time soon.
As wolfpup says, sugar+potassium nitrate are all you need. I’ve made some in my garage. It’s not the most energetic propellant, but it’s substantially better than black powder (another low-tech propellant).
Iron Dome doesn’t intercept all the Hamas rockets it detects, only the ones that are threatening a target. If it’s heading for an empty field, they just let it go. And you can hardly compare Israel’s resources with that of a band of rebels.
Many of the rockets may be home made stuff, but the ones that reach toward Tel Aviv are made in Iran, China or Russia, and smuggled in. Egypt went to arrest the smugglers the other night , dozens kills. The smugglers retaliated with a terrorist attack, vainly aimed at the Egyptian base but it hit a house and killed a civilian girl. Other Egyptians have been killed in the last week.
The terrorists also tried to shoot the missiles from Egypt. One fell short into an Egyptian town and killed four boys.
The sad thing is that the aid money will now flow, there will have to be money spent,
the power station will need experts and trades people to rebuild it… Hamas will be able to tax expenditure and otherwise profit from the influx of money.