First off, if you're making minimum wage, then that's on you. Think about it...your employer is basically saying that we think you're worth the minimum amount required by law and we're only paying you this much because we have to. Their statement to you is this...if you can find something that pays better, offers better hours, etc. then you are free to go.
Secondly, the whole supplying tools thing has always perplexed me. There aren't too many jobs that require you to bring your own equipment. I am sitting at my desk, and I didn't bring my computer, or it's software from my house. What's even more baffling to me is the amount of money spent on tools off the truck, or even online or at box stores. The average mechanics salary is $36k, or just over $17 an hour. When you figure in the cost of tools, the fancy Snap On/Cornwell/MAC/Matco box, what are you really making? It's nuts.
http://www1.salary.com/Automotive-Mechanic-I-Salary.html