They are super expensive. The ones we use at school are Tektronix. Some are $20k, wowzers! Anyway, the ones we use are pretty awesome and I would recommend getting one on the used market.
Overall, I would buy something second-hand that has already been tested and calibrated. Also, get one with a digital screen. You may want one that can record data on an SD card or something too, for future reference. Also, make sure it has several inputs.