Eastern Europe

Does anyone have any info on travel from Prague to Transylvania? We are still trying to find the most the least expensive place to visit while on our short stay in Eastern Europe in September. Arriving in Praque we will have only 7 days and (very very little cash with our pretty worthless US dollars) and would like to leave Prague asap to visit a lovely country/city elsewhere.
One country that came up is Transylvania and Romania. But is it too far for such a short stay.Any ideas or tips?
Thank you in advance!
Best Regards, Debra