How much does it cost to start a tow truck business?

speak to other people in the industry, and also check out your local or federal government website as they all have a section for new business which will help you understand the administrative costs such as business registration, taxation, etc...

Do your research first and make sure you do a course in small business management. Some government agencies offer these courses for free. People that don't do some sort of business course nearly always fail in the first few years