Strong desire to start a business

As the title says, I have a crazy strong desire to start a business. I have wanted to ever since I was young - I have always wanted to design a product and sell it. I am currently a senior in college studying mechanical engineering and currently work at a tech startup. My question /problem is twofold. One, I want to design and build something but I just don't know what. And two, I don't have a ton of money to throw into it. For those of you who were in a similar situation, how were you able to figure out those two things?

And if you have any ideas for a product I'd love to hear it lol.