This particular Thursday, the official rate was $2942 pesos for one dollar. The dealer gave us 2800 pesos for each dollar. All pesos turned to be real, no counterfeits.
You also can exchange money at the Rumichaca Bridge, on both sides of the border, around the immigration offices. There are dozens of money exchangers, men holding stacks of dollars and pesos, offering to exchange your US dollars for Colombian pesos and vice versa.
Change $10 or $100 in one transaction, so it's easy to figure out, otherwise check and re-check the math with your own calculator.
Cafe de la Baca, Garden cemetery in Tulcán.
Crossing the Rumichaca Bridge by car, buying SOAT
The road between Ipiales and Pasto
Returning from Colombia to Ecuador