Nick - you could catch the bus from Plovdiv to Pamps. The bus runs from Sofia-Plovdiv-Asenovgrad-Bachkovo-Narech. bani-Hvoina-Chepelare-Pamporovo and then on to Smolyan. The cost is about 18 levs one way
Also, a good friend of mine does airport transfers (and car hire). He will drive you from/to the airport and leave the car with you in Pamps if you want car hire as well. He is based in Smolyan so I will get a price from him if you are interested.