If you stay @ Molay Idress you might consider wallking back and forth. It will depend on you, teh weather and time of the year but it is very do able. It is about 4 km each way. Your other option is to charter a Grand Taxi for the bus station it should cost you no more than 30 dh for one way. you can walk once you are done or you can ask the driver to wait for 2 hrs and give him like 50-60 dh.
If you are coming from Meknas than take a grand taxi to Moulay Idress for 10 dh and follow the above plan
Volubilis - you can cab it. You hire the grand taxi for the day which you catch at the train station - I paid around 130 DH... You probably won't find too many other people going out so you may have to commandeer the whole thing. As always, lock the price in BEFORE going. Haggle here.
(My personal choice for Volubilis transport is renting a car)
The route involves taxi from Meknes to Moulay Idris (30 mins) to Volubilis (5 mins).
The taxi stand in Meknes is in the Ville Nouvelle. Grand taxi which can take up to 6 people charges DH10 each one way. The front of grand taxi sits 2 person. From Moulay Idris, you may have to charter your own taxi for for DH30 to Volubilis as this route only for tourists. When I retunred I walked but it took 30 mins + a climb up to Moulay Idris as it is located in the mid levels. Good exercise.
Volubilis is at 31 km from Meknes. From Meknes there's a lot of "grand taxi" waiting for you. The ride is 30 minutes and should not cost you more than 150dh.
Don't forget to deal with the taxi driver!!!
You can also go buy train from Meknes to Moulay Idriss and from there take a "grand taxi" (only five 5km).
Meknes is a big town so there's is a lot of train connection from every town in Morocco.