Help: new lense for Minolta QTsi Maxxum

Hi I have a Minolta QTSI Maxxum camera and im looking to upgrade my lense so I can zoom in to a range anywhere from 200-300mm. I have called camera shops and they have told me that I would probably have to buy a sony lense that is expensive. does anyone know a good lense that is under 200 dollars that would be good for general photography and would be compatible with my camera (I take photography at school and would like some versatility). Please help me out. Thanks.