I just looked up a random ASIC, it consumes 1350W and costs 2500$. If you would buy an electric heater, you could get one for 50$. ASICS produce heat, but are not made for heating. ...but the PCB inside can release some nasty stuff, so it is not advised to use it as heating.
The reason ASICs cost so much is because of the upfront designing, tape-out, and testing costs and because they can get away with it because bitcoins are so valuable. The actual costs of making ASIC's are very cheap after the design if completed(few dollars per wafer dependent upon the quantity).
There is nothing wrong with using PCB's in heating if the right materials are used.
Economics will force either ASIC manufacturers themselves to start introducing these products or we will crowdfund the operation directly to force them to start and compete with these products.
I personally would only use it for heating with a heat exchanger, not the air directly that it is blowing out. No matter how safe they are claimed to be.
The price you pay for an ASIC is just like any other high tech equipment, the actual material might be cheap, but you pay for the technology and knowledge behind the device. And as you said, YOU have to pay for THEM for investing in million $ manufacturing equipment, personnel etc. and this price is distributed in the price of ASICs.