I am building a power monitor project, and I want to measure the current flowing through the 230V mains supply to my house non-intrusively. I am aware of AC current clamps/transformers. I also came across hall effect current sensors like WCS1500. I've also thought about making my own current clamp. I'm not sure which is the cheap and efficent way to do this.
Depending on what the goals of the 'project' are, so what you build or buy, what you're intending to learn, a split core current transformer is hard to beat.
It can be very cheap if the core is salvaged from a dead transformer.
It's safe, as it clamps over a wire, and while a toroidal core could give slightly better performance, that would need a mains cable disconnected and reconnected to thread it through the core, not cool if you're monitoring the incoming to the house, but more practical if just monitoring a power strip.
As long as you assemble the core with good attention to getting minimum air-gap, it's very tolerant technically.
The output gain is calculable from first principles, knowing the number of secondary turns and having a small enough burden resistor. Compare measured and theory would be an interesting result of the project.
Safety and construction codes are intolerant of 'special' additions to your house wiring, especially to the input side of your breaker box. Standard approaches do exist, and an electrician can install either current transformer(s) (with suitable mounting and enclosure) or a second electric-utility-type meter. Some of the 'smart' meters run Linux and report by radio OpenWay Meter.
Usually, insurance and local ordinances will mean that inspectors and licensed electricians will be involved. Your local electric utility will probably have to be consulted if the meter is to be pulled (detached) during the installation.