I don't think that is receive only, there is an active radar. The iron drone system seems catered to detect mortar/missile/UAV rather than consumer drones so it's certainly overkill and could be done for less.

Drones and UAV can cost more than $10k in hardware alone. I'm not familiar enough with the sensors and the technology on the detection side but wouldn't assume that anything comes cheap.

There are no product selling in the $10k price range. You will need to go through procurement with numerous sales meeting and demonstrations to make a sale, which automatically push the price to $100k and above.

It's low volume, meaning few units to recoup the development costs. Let's keep in mind that it takes a lot more than a guy in a year to develop a product.