I just purchased a LAS-LAX one way ticket in economy for AUD$98 with United, after purchase I was offered a seat upgrade to First Class for USD$75 more or Economy Plus for $14 more. This only works out to be USD$50 more if I checked one bag in or USD$15 more if I check in two bags for First Class. I took up the offer so in total I paid AUD$185 for a first class ticket which before I booked was about AUD$360. Are these upgrades always offered? if so why would anyone book in first if they could upgrade an economy fare to first for about half the price?