Lookin for a cheap cruise for two senior citizens from Los Angeles,Ca to Rio, Brasil?

I don't think you're going to find ANY cruise from LA to Rio, much less a cheap one. There was one cruise a year or two ago that went all the way around South America, but that was because the cruise line needed to reposition a ship that was too big to go through the Panama Canal.

Most of the cruises out of LA go to Hawaii or Mexico; occasionally you'll find one that goes through the Canal to Florida one way (and then a return trip for a separate fare). And some cruise lines have a ship or two whose home port is Rio.