Historical "low fares" between North and deep South America have been in the $1000+ range for years. Occasionally there are sales that are less, and recently there have been some unheard of bargains. July is very low season @ EZE. However, I don't think fares will come down for awhile, as UA only has one flight a day from the US. Note that EZE can get very cold and bitter in July, on the other hand, it can be pleasant, too.

Do what you can to stay on the nonstops - it is definitely worth a premium, even if the airline isn't premium. I travel to South America frequently, and it will improve your travel experience immensely.

From what I hear, COPA is a very long, yet not totally miserable, experience.