If you have the money, I STRONGLY recommend you get a gym membership. If not, at least buy some dumbbells with adjustable weights. If you only have access to that one machine, it seems like you can only do flies, chest press, and pullups. I may be wrong, but there doesn't seem like you can do many exercises with it. Sell some of your excess computer hardware and games and buy some weights for optimal results.
However, I think the most expensive part of working out is the food! I'm 5'6" and 155lbs and I've been trying to put on a few extra pounds with a 3000 calorie diet, but man! it's so expensive to buy so much food! Protein shakes make it a bit cheaper than buying meat, but still...