Dan Hassenplug’s monthly expenses used to include around $300 for lunch and three or four books bought from Amazon.com. Now he’s plugged into a new breed of social network that helps him manage his finances. “When you see a graph that says you averaged $10 a day for lunch — about $300 for the month — well, that’s a lot of money,” said the 24-year-old design manager from Geneva, Ill. Now he’s cut that expense in half by packing a lunch most days and buying only one book a month. “There’s a library down the street,” he said.
