It depends.... if you want a 1on1 tutor, they normally cost about £15 per hour.
A night class would probably save you money and you may be eligible for part of your course to be paid for you, depending on your financial situation, where you live, etc.
There are online resources to get you started...
http://www.bbc.co.uk/languages/spanish/talk/
http://www.123teachme.com/learn_spanish/beginner/
http://www.studyspanish.com/freesite.htm