I'm not in the market and clicked the link out of curiosity, but yes, I can turn my android phone into a hair dryer if it takes $35 of auxilary equipement.
I'd love to see that actually... Most hair driers are very power hungry. 2kW is not uncommon (at least here where standard voltage is 240V). Achieving substantial amount of drying from a mobile phone battery would be quite a feat of engineering.
Make a small rechargable hair drier for camping/use where outlets are in short supply, and you've got yourself a saleable product, even it it only gives about 5 min of hot air.
If battery powered, it would be a very expensive device and require a big heavy battery.
Power tool batteries, eg a dewalt 18v drill, allow a max discharge current of around 10 amps. So for a 600 watt hair dryer, you're going to need 3 power tool batteries! Imagine the cost/weight of that!
To make it work without the high cost/weight, you're going to have to blow mostly cold air and hope the user is okay with that.
