Actual cost - Teacher Home Swap costs $100/year vs. hotels which easily cost $100/night before tax, parking, etc..
You will be welcomed into the community, not just a tourist. Making a swap with a community member who is actively engaged through teaching will provide you with a more fulfilling travel experience. You can use your teacher swap partner as your personal connection (for ideas, introductions, and insider knowldege)
A potential downside to swapping: you have to clean up after yourself. However, there are a number of options for hiring outside help on this if you are not excited to do this.