How to find the cheapest flight when your schedule is totally open?

I am currently in South America and i am open to taking bus or flying from Peru to Colombia but i was curious if anyone knows of a way or website that allows you to say. “Give me the cheapest flight in April from Lima to Bogota.” For example. I have seen some online website say “my dates are flexible” but if it is for international flights the option is disabled. Any ideas? Thanks

Website such as as Expedia, Orbitz, and Kayak have a function that allows you to search under flexible travel dates. Usually you just click the option “flexible travel dates” or whatever wording the site uses. This is a great way to go because airfare is much cheaper certain times of the month and certain days of the week. In terms of international flights sometimes the websites don’t work as well. If the website still won’t work call a customer service rep for free and they will definitely be able to help you. Good luck and happy travels!