The money changers are clustered on the corner of the Parque Isidro Ayora in the Ecuadorean border town of Tulcán. Under the morning drizzle, six of them are tapping furiously into book-sized calculators and peeling off thick wads of dollars.
They are working the steady stream of Colombians climbing out of mini-vans, fresh across the border two miles to the north. Business is brisk and there is little give-and-take on rates.
Colombians of all stripes come, from couples window-shopping for wedding rings to determined housewives heading into minimarkets to load up on staple foods.
Encouraging this flow is the weakening US dollar, Ecuadors currency. After a severe financial crisis from 1998-2000 and a run on the sucre, Ecuador adopted the dollar in 2000.
As the greenback has sunk against Latin currencies, Ecuador has become steadily cheaper for its neighbours. Four years ago a dollar bought 2,909 Colombian pesos. Today it fetches just 2,185 pesos, a 25 per centfall.
In one of the many battered shared taxis, Miguel and Juana, a Colombian couple in their late 60s, are heading from the Colombian town of Ipiales to the border.
This is not the first time they have made the trip. They are going to Tulcán to shop for bedclothes and have their eye on an eiderdown, as well as mens clothes. They are middle class and dressed in their Sunday best: Miguel is wearing a sports jacket and Juana has pencilled-in eyebrows. Miguel says they go over to Ecuador more often now but Juana complains that the quality of some of the Ecuadorean clothes is questionable. They have a keen eye on the direction of the dollar: Miguel concludes its going to get weaker and predicts they will increase the number of journeys they make.
After border formalities, a fresh rank of Ecuadorean- shared taxis waits to take people to Tulcán. Round the corner and just out of sight of the border guards, a line of men, adolescents and kids in tatty jeans and stained T-shirts, stand with an array of plastic jerry-cans. They are selling petrol to Colombians. This is the biggest bargain of all: thanks to Ecuadorean subsidies and the dollars weakness, petrol costs just $1.48 a gallon in Ecuador versus 6,500 pesos or $3.08 in Colombia.
These men are the small fry, sniffs Gabriela, an Ecuadorean whos on her way back to Quito. There are tracks across the border that are virtually unmonitored and smuggling is getting worse, she says. Others claim that some Colombian cars are fitted with double tanks to assist the illegal trade. Some estimates of the scale of petrol smuggling run very high: César Robalino, the president of Ecuadors private bankers association, estimates that as much as 40 per cent of the countrys petrol is being smuggled out. Petrol that once seeped out of the country is pouring out, with the bill being paid by the Ecuadorean taxpayer.
The border bargains are drawing people not only from Ipiales, five miles away, but from Pasto, the capital of the department, 82km away. Theres a brisk trade in gold jewellery but in general, its the mundane rather than the exotic that is most sought after.
In Tulcán, tins of fish and fruits, and displays of chocolates and toffee are on sale in the mini-markets. Prices in Colombia are between 20 per cent and 50 per cent more for basics.
Not everyone is persuaded that the trips are worth it. In Ipiales, hairdresser Sandra Bastidas says she goes to Ecuador only from time to time. She finds that with the transportation costs ($1.50 each way), occasional lines at the border and the small amount that she can carry with her its not worth going more often.
Even if it offered more savings, the trip is not particularly enjoyable for Colombians, she says. We Colombians have a bad reputation. Ecuadoreans assume were smuggling drugs across, hidden on us, in our clothes.
However, those that make the trip appear to be spending freely. And it is surely no coincidence that the streets of Colombias Ipiales are nearly deserted on Sunday while Tulcán is heaving with Colombian shoppers.