My 2001 hyundai tiburon has been shifting very hard for a days. We would have had to turn the car off and?

then back on again, berfore it will shift. when it would shift after initially turing it on it would pop into gear and chug the car. today, the day before we were to take it in, it made a small squeel and then it shifted to 2nd twice and that was it. Now it won't shift at all, and doesn't go in reverse. The fluid was in need of change, which we were going to do tomarrow but is full. We can still drive the car but can't back up and can't shift. the engine light came on on thursday and then went off three days ago (Mon). Now it is thursday again and we can't shift, but the check engine light has not come back on. does anybody know how much a new/used transmission is for a tiburon and if it needs to be replaced? What are the symptoms of a failing transmisson. Thanks so much for you help.