You don't have to spend a ton to vacation in the heart of Austin. The Firehouse Hostel off of 6th Street is the place to be, thanks to its setting in the center the city, close to nightlife and awesome restaurants.
Make a point to load up on the hostel's free daily breakfast, and then cook in the communal kitchen to save money on dining out. When Austin's food scene is too tempting, grab an Amarillo Burger (serrano chiles, jalapeño Jack cheese, and cilantro mayo, $12.50) and a $3 PBR tallboy at Casino El Camino.
When you're ready to get out of the city, head to McKinney Falls State Park ($6 entrance fee), and take a cooling dip in Onion Creek.
Lodging: $31/night for a bed in a shared dorm
Food: $30/day for groceries or a cheap meal out
Activities: $6 for entry to McKinney Falls State Park