I just worked out my budget for this coming year. My rent went up to $795, which is fine, because its a nicer apartment and very close to school (not worth packing everything up and moving to save $20 a month). The town I'm in has their own power company, so thats $15 a month (in the summer with generous air conditioning). I've got my internet bill for $30, don't bother with cable tv because the only things I watch are on ABC, Fox, NBC anyway. Generally food is under $120 a month, but I budget it for that much to be safe (taco salads+rice, pasta, stir fry ftw). I also over-budget gas at $100, since I normally drive less than 5 miles a day, so that also covers me for oil changes and the like. Now divide all of that by 2, because I split with my girlfriend. I'm still on my parents insurance, so I can really say I'm living off of $600 a month. I still allow myself more than this obviously, because I'm in school and you don't stay home all the time (sure sometimes I'll drop $50 on drinks, not the best decision, but it happens) and I usually find some nice gift to get myself every year (sweet guitar last year, PS3 this year).
But really, anybody who says you can't live off of 20k, its very unrealistic unless you're in a major city. My dad is a high school teacher, and my mom is a dental hygienist, so they make around 50k combined, and have a good sized house, acreage, go on at least a few vacations a year. Sure I know people who make $80k and are broke, but they hit up Tim Hortons or Dunkin every morning, have an iPhone, eat out almost every night, buy a new outfit every week, etc. The simple ways to save and spend money are what really gets you.