Good advice so far, just settle for DIY CO2 or Excel for now and if you do need to sell the tank know that it being an ADA will allow you to get full price for it less the shipping costs you paid. Just stipulate that it is in flawless condition and advertise on Craigslist in a 300 mile radius - you'd sell it fast.
I went through a period of being poor about 8 years ago and learned lots of money saving techniques that keep my pocket full to this day. One of the big ones is to get yourself a PuR dispenser DS-1800Z and get used to drinking nothing but filtered tap water. It's not only much cheaper but healthier as well, breaking yourself from caffeine addiction is the hardest part - just use tea to abate headaches until you can free yourself from it completely and you'll find yourself sleeping better than ever.
Learning to cook from scratch can save you lots as well or at least only buy things that are on sale 2 for 1 at your local foodstore - go weekly and buy in bulk the things you eat regularly to last until the next sale. Everyone needs internet but ditch the cable TV - you can fill all your media needs online and life is way more peaceful without the constant bombardment of commercialism and propaganda.