https://autocaresjulia.com/pdf/horar...montserrat.pdf

There is a private bus operated by Autocars Julia that has a morning bus departure adjacent to the Barcelona-Sants station and deposits travellers at the entranance to the monastery, skipping the Aeri and Cremallera. The ride takes about 90 minutes. The departure back is in the early evening.

Pros

• Fastest option, overall travel time
• Most comfortable option

Cons

• Only one daily departure each way
• Using the bus in both directions is a very long day in Montserrat
• Less scenic than the Aeri and Cremallera

There are also private tour packages that can be booked online or in Barcelona (I went to a Tourist Information booth across from the Passion entrance to the Sagrada Familia to get information and tours could be booked through them). The packages include train or motorcoach transportation to/from Montserrat, entrance fees, and a meal in the cafeteria. I didn't look into this as I was linking up with a guided tour that covered my admission fees; all I had to do was be at the monestery by the tme the group arrived via their private motorcoach.