Palma Mallorca to Sóller and return is 17€ one way is 10€
http://www.trendesoller.com/es/cms.php/horarios

I think that's plenty of time for Soller and Deia.
Jane

The tram in the the port takes only about 10 minutes and the port iteslf, like Soller is quite small. A lot of the shops will close in the afternoon for siesta so 3:30pm might turn out to be stretching it a bit. A couple of hours in the town and an hour in the port is probably sufficient so maybe 2pm at the latest is about right.

Similarly Deia is very small and will only take a couple of hours if you walk up the hill opposite La Residencia, the well known hotel. This takes you up to the church which takes up a fascinating half hour (no sarcasm intended--it does only take half an hour round and in the church and it is fascinating).

All three places are well worth the visit and if possible, make time to see Valdemossa during your Mallorca trip.

Would it be better to get off the bus at Valdemossa, and see Valdemossa or Deia, if I only have the one afternoon? Can you walk from Valdemossa to Deia then catch that bus? (I'd love to fit 1-2 hour hike in somewhere, but I'm not sure where...
Any Mallorca tips are greatly appreciated! Food recommendations?

The road distance from Valdemossa to Deia is given as 6.5 miles on via michelin, so it is walkable in a couple of hours tops.

I wouldn't want to miss the ride on the train to Soller though, so if you have only one afternoon, the walk is a step too far. Why not take the train to Soller, early as you suggested, then bus to Deia, then bus to Valdemossa. You can then take the bus back into Palma to finish your excursion.

We're definitely doing the train to Soller, and tram to the port- we just wanted to fit in a hike before heading back.
I'm thinking we'll just stop in Deia and walk around for a couple hours then head back.
The next day we're going to do Palma Le Seu, and Bellver Cathedral, etc. Are the open-top buses for that worth the money?

We've done the HOHO buses and remember that you get headphones and a choice of languages. The Cathedral is close to the centre of Palma and dominates the view over the sea in that part of the Paseo and you don't need the bus for it. Bellver castle is worth the visit with views over the marina and the trip will give you a general orientation of the city.

I seem to remember that it may have been around €15 each, so if there are 4 of you, a cab might work out less expensive. Negotiate a round trip fare with the driver first. An open top bus does give better views as you drive round.

We enjoyed walking around Valdemossa more than the Soller destination, however, we still enjoyed the Soller train ride and enjoyed the scenary along the way. We took the bus to Bellver castel and when we arrived it was sunny, and 45 min. later a huge lighting storm came in suddenly and left us stranded on the outside of the castle. This was late Sept. A bus would arrive and no one would get off because of the storm and we had to wait until the next bus. We were soaked and had to sit in the open upper deck with water running like a river down the isle. The bus driver had to yell at the people to move back to let us in to get to the upper deck. On the outside of the castle many us felt vulnerable to the lighting. It was a very unpleasant experience and put me off using those buses.