3D printing for product ideas?

[JetFalcon]

I am considering getting into 3D printing because I have a product idea that I want to design. It's very simple in how it works, but I think it would be a great car accessory to try sell on the market, I see it as something simple you may buy at the car wash since they always sell impulse buy car accessories. But it's just an idea in my head but I really want to go the next step. I will at least want to build a prototype that's easy to make through 3D printing, just so people can get an idea what it will look like. But then wondering if 3D printing could actually be working units or are they only for show? I could possibly buy those cheap $300-500 ones, but then I think something at my degree would need the professional ones so I have the space to build bigger things.

I don't know how to use graphics program, but I learned how to fly a drone. So wondering how easy it is for a normal non geek who only uses the computer for the internet, some excel stuff, and doing basic office work like quickbooks to pick up a 3D printing program. Or is it possible to join a free or cheap lab like through an educational system that will allow me to learn 3D printing?

I just want to design something pretty simple, just a rectangular shaped item. And I'm hoping 3D printing won't be expensive or hard to learn, maybe something I can do within a month if I commit? What can 3D printing do for me if I have a product idea that's just in my head?