Comparing Oranges to Oranges?

This morning I was in need of an orange for a recipe that I am going to make next week. I dropped by the local Wal Mart Super Center on my way to work to purchase it. I was in for a couple of surprises. First off, I was going to purchase one orange. The price for one naval orange was 75 cents! After recovering from the sticker shock, I decided to buy a bag of oranges. I could purchase a bag, with about 7 or 8 medium oranges for around $3.98. Upon closer inspection, I read the sticker that said that these oranges were from SOUTH AFRICA! Next to these bags were a bag of 7 or 8 oranges that were from Edinburg, Texas. These oranges were $6.98! Now, my husband and I met in college in Edinburg, Texas. It is a lovely border town in Texas. You know, Texas which is part of the continuous states in America. I simply cannot understand how the oranges from South Africa are priced more affordably than the ones from Edinburg, Texas.
I am just wondering how this is possible?????