Perhaps I misread the question, so taking Heathers reply to the next level........The cheapest option would be to steal a taxi, and drive it yourself.
The original post was 'how much would the trip cost in a taxi?', not 'what is the cheapest way of making the journey, and how do I cover my a*se if an uninsured driver smashes his car up with me in it?'.
Personally, I would go to the party.....get totally paraletic....stagger off to the beach to sleep it off....and then get a bus home the following morning.
But that might not be the answer for everyone.