I have used several of the mid-priced Grado's and have been content with them. I currently use a Benz Glider M2 and find it to be much better than the Grado's or the Sumiko's I have had over the last few years. I know the Benz can be had used for about the price range you are in.
Keep and eye out for a Shelter 501 too.
Keep and eye out for a Shelter 501 too.