yo mrd - keep the faith
if it's mainly a case of disproportionate amount of fat on your chest (little to no glandular tissue, nothing fibrousy), keep going to the gym in your spare time (or if you don't have the time, make time).
i know spot-reducing fat is a myth (or so they say), but working out/cardio will help you reduce fat all over, which includes your chest area. also continue to build muscle (not just chest but all around), as that increases testosterone, which in turn helps with fat burning and overall muscle development/tone. that may also help the chest issue. and plus, the endorphin release you get afterwards is a nice high... (also, at 18, you're still increasing t naturally, so that might help with muscle development and fat reduction, too - who knows? maybe when you hit 21/22, you won't even need surgery)
also keep in mind that you've got this body forever. you're still really young - and in the grand scheme of things, a few more years of saving money is nothing. sure, your youth is supposedly the "peak" of your life, when you should be going to the beach with friends and partying with your shirt off or nonsense like that, but the flip side of it would be not saving, not getting the surgery, and just feeling miserable for not having gone through with something you've wanted for yourself...
which brings me to the next point - as you're saving, slowly start appreciating other things about yourself that are great. i konw that sounds hokey, but i think it's really important. surgery can help tremendously, but doctors aren't miracle workers. keep in mind that, even after surgery, your chest may not be perfectly flat or perfectly "normal" (though it'll certainly improve)
i'm in my twenties, had the surgery last week after many years of contemplating/researching and even more years of hating my chest. i've said in other posts on these boards (and i'm sure i sound like a broken record), that i think it was worth every dime, not necessarily because of the final results (which i won't really be able to see until a couple months out), but because i finally came to terms with the reality of it all, with the peace knowing that i've exhausted even the "last resort" surgery option for "fixing" my chest...
my chest definitely looks flatter, but i know (and i knew going into it) that it would never be up to my standards of a "normal" guy chest... but i'm extremely glad i went through with it.
just continue to save your money with the knowledge that surgery can help you improve what you already have and bring you more self-acceptance. but don't overextend yourself and juggle tons of jobs and school just to get the $5000 soon, thinking that it's going to be a completely life changing experience.
think of it as something you need to do for yourself - not for the ladies or to get dates or for anyone or anything else. and there shouldn't be a rush on that since you'll have yourself for your entire life.