Empirical evidence justifies or disproves a claim. A single point of data does not justify the claim that vegetables from Mexico are cheaper than vegetables from the EU - all you have done is state that you once found a vegetable from one source country for cheaper than the same vegetable from another country - you haven't provided any evidence what-so-ever (the name of the supermarket, the prices, the volumes, the different brands), just made a claim.

Empirical evidence in this case would be a large scale survey of the prices of comparable vegetables across multiple supermarkets, over a long period (several years to cover seasonal variance in prices).