Last Minute have a very good set of tours. They were offering €40 per person for the whole Island tour recently.
The Catamaran tour is good, there are buses from Costa Teguise direct to Puerto Calero. Also a few trips leave from Puerto del Carmen. Try
www.arrecifebus.com for times and prices. Very reasonable.
Other options are to ´phone from a call bo (very cheap) and most tour companies speak good English.
The FIRE MOUNTAINS are a MUST!