What is the local currency?
The local currency in Spain is the Euro
Should I change money before I go?
You can change money in advance or get cash out of an ATM, the exchange will be at the rate of the day. The ATM and your bank may charge you for these transactions.
How much should I budget per day for extras?
Around 25 - 40 USD a day should be plenty, but this is guidance only as you know your spending patterns better than we do.
Is it customary to tip?
Yes, but it is at your own discretion. If you are happy with the service it is nice to leave a tip, around 10% in restaurants and bars.
Then for your guide and driver, it is customary, though not compulsory to tip them around £5 - £10 a day, this would normally be given at the end of the adventure and is completely up to you and whether you feel they have earnt it.