Traffic sources for CHEAP TESTING

Hi, regarding affiliate marketing: you need to test until you find a profitable combination of offer an traffic souce. Probably there are differences between the traffic sources. In one you need more money to test in another less. So my question is: in which traffic sources can you test an offer WITH THE LEAST AMOUNT OF MONEY? With “test” I mean that I need to see if it the campaign is/can be profitable or not.

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