Ticket fare varies anything from Rs300 to Rs1500 or more based on the type of the service.
The cheapest is obviously the Rs300 or so non AC type bus.
If you are keen on a bit of extra comfort book in one of those multi volvo buses. Ticket costs around Rs800-Rs900 per seat.
Also you've the option of going for sleeper buses. AC Volvo luxury type service should cost Rs1500 upwards a seat/berth.
There are quite a few reputed operators to chose from like Neeta Tours (neetabus.in), Laxmi Travels (laxmibus.com),VRL Travels (vrlbus.in),Shree Krishna Varun Travels (skvbus.in),Paulo Travels(phmgoa.com), Gogte Travels (gogtetravels.com), Kadamba (Goa State operated) , MSRTC (Maharashtra State operated) etc
Also note some bus services are with real time GPS tracking of position feature. Saves you a lot of time in managing the waiting and boarding timings.
Most of the buses are overnight services. Pune to Goa (Panjim) should take around 10 hours.
You can book tickets either the through the bus operators directly or through thirdparty reservation portals like redbus.in, cleartrip.com etc.
And lastly check out the bus destination at Goa. Most of the buses end at Margao via Mapusa and Panjim.
Those who are planning to self drive, check out the various route options and maps to travel from Pune to Goa. Also if you are driving from Lonavala to Goa, see Mumbai to Goa via NH4 for driving direction.