Abs light and brake light on. Vehicle shakes 30-70 MPH?

Hello, I drive a 1996 Ford Aerostar and about a week ago my ABS light and brake light came on. They only come on for a couple seconds, right when I start up the van. Then when I am driving and I get to speeds between 30-70 mph, the van begins to shake a lot. I checked my brake fluid and it is a little under the max. Does anyone know what could be causing this? And if I can fix it at home or will I have to take it to a shop(and how much $?) Thank you.

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