Always in pesos, cash or Visa or Mastercard. Current price as of August 6 is 196 pesos. TAPO to CAPU terminals.
Is that the "walk-up" price on the day, cheaper than I was expecting! :-) I did wonder if there was a fixed maximum price for tickets purchased for immediate travel or if it goes up in price in accordance to demand.
The Estrella Roja bus from TAPO to CAPU costs from $176MXN and runs every ten minutes. No need to prebook. ADO buses are more expensive depending on level of service and run approx every 20 minutes. Prices do not fluctuate. On longer routes there are sometimes online discounts but the ADO website does not accept foreign cards.
There is also a bus from MEX to Puebla: this drops off at 4 Poniente, which is much more central than CAPU.
I paid MXP198 (you have to pay in Pesos) on Estrella Roja from the TAPO to CAPU for Primera Clase. Normal class is MXP178. You need a taxi from CAPU to downtown which is about MXP78and be aware the taxi queue is a long wait!