With little to no budget, finding filming locations is not as simple as renting a sound stage and building sets. You need to use your connections, be creative, and ask for help.
Here is how I found locations for Slim. I begin with the simplest step: my own house. The living room served as a large, fancy bedroom. The empty garage worked as a detention cell. We used the driveway for filming interiors of vehicles. The backyard worked for wilderness closeups.
My friend Mike had a large property with a massive backyard. I believe it was seven acres and it took his Dad five hours to mow it. I asked any friend that owned a tent to bring it and to set it up in a group. This became a wilderness encampment. His backyard from another angle looked like another location. Behind his backyard was woods. These became a rainforest. Further beyond the woods was an un-mowed field, which worked for other scenes. Inside his kitchen was a corner booth, which became a restaurant. We even had a scene at his pool.
My Dad's office was used as both Slim and Dr. Colossal's offices. The manager of his building allowed us to film in the alley around the building as well. My friend Rickey had a large spare bedroom, which became a hotel room. His family's restaurant was used in another scene. My friend Alissa had neighbors with an incredibly long, dirt driveway, which became a roadway for a chase.
Some family friends had a bar built into their downstairs. It made a great ticket counter for an airport and, with some redecorating, became another airport. My friend Greg's house had very large rooms, which worked wonderfully for a mountain villa. The undeveloped end of his street was a perfect country roadway. A public park worked well for wide shots in fields. A family friend is a manager at Wendy's and allowed us to film there. We used a local gravel pit for a desolate wasteland. Back roads near a friend's camp were perfect for a car chase. A popular sledding hill in town became the top of a mountain.
As I count it, that is about 25 different settings without a single dollar needing to be spent. I would say that is a good investment. Having no budget forces you to be creative. People are very generous and willing to help, you only need to ask.