All of the suggestions above are great, but my favorite site to monitor airplane tickets is kayak.com. This site allows you to check hundreds of sites (expedia and cheaptickets too). Plus you can check hotel costs and rental cars. I love this site becasue they are not the sellers, they just monitor the industry and then tell you where to get the best prices.
just keep looking and prepare to be flexible on your flights to get the best deal. sometimes packages and charters are less. Try a travel agent for charters. good luck. It still could be 500$ PP round trip! try out of Chicago for a little less expensive.