Just follow everyone going toward passport control. You will all go down an escalator or stairs. Turn to your left at the bottom and you will see the booths for paying. You can't really miss them.
The US recently raised the cost of an application for a visa to the US to US$140 so the charge here will also change. Argentina put theirs up already. So it is hard to say exactly when it will go up from the US$131, but go up it will within the next few months.
If paying cash, use clean bills with no writing on them and no tears. You can also use your credit card.

Be sure NOT to follow the crowds to immigration. We noticed several people who waited in the immigration lines, only to be sent to pay the fee and then wait in line again. We did the same the first time we visited Chile. As Huentetu said, there are signs at the bottom of the escalator, but I recall that they were a little confusing. They have pictures of flags from the US, Canada, UK, and Australia and an arrow that directs you to the booths on the left, but no clear instructions in English that indicate that this is where you pay the fee. The rate has already gone up to $140, but is good for the life of your passport. I believe we paid $90 several years ago when we entered. Chile's a great country, so if you're hooked like we were, you will return. When you split the fee over several trips, it doesn't seem so bad. After you pay, you must get in the immigration lines.

Thank you much for the info.

On one of my trips to Chile a few years back, there was a family of several people sitting near me. Middle of the night, I was awakened when I heard the dad yell out, "What??? We have to pay all that money when we land???" I don't remember if it was a family of four or five, but it was going to be at least $500 to fork out the moment they landed. He'd been leafing through his guidebook on the plane trip down and apparently had just come to that part.

The advice to follow the crowds is sound, assuming that you use some sense and find where to pay before you actually join the immigration line. The line is to your left at the bottom of the escalator, and the payment booths are signposted much further over to the left--effectively a U-turn to the left. Go there first then return to the main immigration line.

If your plane happens to be coming direct from Lima, say, don't follow the crowds, 'cause they all get to go straight to immigration. So look sharp left for the red ropes. And you might have to wait for someone to show up before you fork over your $140. Just sayin'.

Not that I would have gotten lost or anything.

I don't seem to have been clear enough. You are all heading TOWARD passport control/immigration. You will all go down the escalator/stairs. If you need to pay a reciprocity fee, you will turn sharp left, virtually a U turn, at the bottom of the escalator. Everyone else will get into line for immigration. When you have paid your fee, you will get into line for immigration too.

Thanks -- very helpful info

Am I correct in assuming that there is no reciprocity fee if one arrives by sea (cruise ship)? How about departing by land?
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Vic's travels: http://my.flightmemory.com/vogilvie

I assume there will be signs directing one to where to go to pay the reciprocity fee?

Vic, no fee arriving by ship.

yestravel, yes signs. Look out for them at the bottom of the escalator/stairs just before passport control. I won't be more specific in case they redecorated!

Believe me: If you get to passport control without having paid the fee, they'll point you back to where you have to go.

Thanks! I have no doubt they will send me there if we miss it, just trying to avoid backtracking after a very long overnight flight.

If it's still the same as it was in July (and I don't know why it wouldn't be), it's a VERY sharp turn after you get off the escalator; almost a U-turn. I know, because even though I was looking for it, I missed it the first time.

I am going to Mendoza, Argentina by way of Chile. I'm not real familiar with the reciprocity fee. Please explain. Also, do I have to pay anything when we arrive at the airport in Mendoza? This is my first trip out of my country (US).

If you enter Chile at the airport in Santiago with a US, Canadian, Australian, Mexican or Albanian passport you have to pay a reciprocity fee. The amount varies by nationality. But if you are just staying in transit in Santiago and have your luggage tagged through to Mendoza, you will not have to pay it. Argentina has a reciprocity fee as well but only cllected at the two airports in Buenos Aires. Flying into Mendoza you will not have to pay it.

Amy, there has been some extensive work on the airport recently, but no doubt you are correct and the reciprocity fee booth is in the same place.

Thank you, Huentetu

question anyone...if traveling by bus ...la paz, bolivia to Arica, Chile do i have to pay the recipocity fee? i cant get a direct answer. ive ask 4 consulates here in the US and they give me mixed answers. ONLY a SAntaigo airport, all airports and ship/bus and airports...im only concerned via bus. thanks in advance. answer asap please. thank y'all! btw US citizen tourist