Passengers that are citizens of certain countries must to pay (in a desk just before immigration/Policia Internacional) the so called Reciprocity Fee, thay it is applied to citizens of USA ($131), Mexico US$23, Canada (US$132), Australia ($61), Albania US$30.

It is the Reciprocity Fee per Person
Yes, that fee it is per person who entry to the territory of Chile with a US passport. That fee allows re-entry in Chile without any other payment until the expiration of the passport.

Why it is Applied the Reciprocity Fee ?
It is something really anoying at the same time fair. When a citizen of Chile wants to visit the US needs to pay $131 just to ask for a visa, if it is refused there is no refund; furthermore, it is neccesary to pay another $14 to buy a special phone card to reserve the date and time of the interview (waiting time up to 2 months): http://santiago.usembassy.gov/OpenDocs/asp/pagDefault.asp?boton=Doc28&argInstanciaId=28&argCarpetaId=&argTreeNodosAbiertos=&argTreeNodoSel=&argTreeNodoActual=#anchorInicioPagina . Not only that, a personal interview it is compulsory in the US Consulate (the only one it is located in Santiago de Chile) and in a country more that 3.000 miles long (around the distance between LA-New York), that it is a real problem for more than 60% of chileans that do not live in Santiago; persons with cell phone are not allowed t the consulate. The result of this it is the unfortunate reciprocity fee and that chileans prefer to travel to Europe (no visa needed) on holiday or business; in fact, right now the main trading partner of Chile is China and there is a huge program of students exchange with Australia and New Zealand.

This is Discrimination
In certain sens it is, but it is the same type of discrimination appied by the US government to chilena citizens, but you get entrance to the country after the payment, something that a clinea citizen do not get for sure.