You can buy a replacement unit from Autozone for around $45. I don’t remember the exact brand/model, but here’s a quick and dirty write up on changing the antenna. Once you get all the parts, it only takes less than an hour to do the swap.
1) Remove front and rear trunk liner. Remove passenger side trunk liner. Behind this is the antenna and related operating motor. If I recall correctly, there is a cad plated bracket that holds the body of the antenna motor in place – either 2 or 3 10mm bolts. Leave these inplace for the moment. Remove the castle nut on the antenna extension at the exterior of the rear fender. The castle nut can be removed w/ a special wrench or the ends of the jaws of small needle nose pliers forced into the 2 holes on the castle nut. Once the nut is loose, screw it out by hand and then remove plastic spacer and neoprene gasket.
2) Once castle nut is removed, remove electrical connector to motor and remove antenna coax. There may be a drip or condensate tube that is attached to the bottom of the motor body that exits at the bottom of the fender well. If so, remove it from the motor body. Remove previously mentioned 10mm mounting bolts. Drop antenna and motor body so extension clear inside of fender, then rotate assembly out. I forget what holds the bracket in place, but you can easily see that once the motor is out. Remove that and its fasteners. You can now get to the intake plumbing, but there isn’t any real reason to remove it, unless you’re getting rid of a few ounces of weight. .
3) Cut the wiring harness off the old antenna. You’ll be wiring this up to the new antenna, makes it easy to install. Connect the wires from the new antenna to the appropiate wires on the Antenna connector diagram below. Please note the voltages are using the stock AM/FM/Cass stereo.
3) Mount the new antenna. They include a couple different angled top mount pieces, pick the appropiate one that closely matches the curve of the car.
4) Replace the drain tube. The old antenna had two drain holes, the new one only has one. I got this from my local Home Depot. I don’t remember what size, just take the old one in and ask them to measure/compare for what you need. I did need to heat up one end to get it onto the bottom of the new antenna.