the dealer is charging around 400 buks for the coating. Is teflon such a cheap material? Morever it seems like a normal wax polish which can be done by oneself.

$400 seems quite cheap when compared to port & polish. l assume that dealer is also flow testing heads as well. The teflon coating must also be baked on before reassembly of motor. The teflon coated ports r much more efficient & run a lot cooler & many claim improved gas mileage. The dimples (like a golf ball) in the coating r claimed to be better than polished & porting with newer fuel blends. l know of six Harleys, two flathead Fords, & a Suzuki dirt bike that have coated ports & all owners claim increased horsepower, better mileage as well as cooler engine temperature.

if it was so damn good,with the price of gas right now,dont you think the factories would be doing it and using it as a selling point ?

Virtually all modern engines are fuel injected. The intake port is simply made larger to flow more air since the fuel is sprayed at the intake valve.
It is not necessary to maintain a high flow rate in the port to keep the fuel and air properly mixed.