This post is over 2 years old now, but for those who may be looking for the same info; I went to Tangiers a year ago while I lived in Spain. I was in Torremolinos and there are all sorts of travel agencies that offer day trips to Tangier! You will find these offers in many of the coastal cities: Malaga, Marbella, Torremolinos, Fueringola, etc. The "package" consists of the bus to Tarifa (it is over an hour ride) the cost of the ferry, and the return trip. I did not have a guide booked, but when you get off the ferry there are all sorts of them looking for tourists. I ended up sharing one with 2 other ladies as I was by myself.

It is a great day trip, I would highly recommend it! Very easy to do and I would recommend booking with one of the agencies, the prices are reasonable. I also would not do the city without a guide. You would NEVER find things. The old city "medina" is amazing! The roads and paths are very narrow and like a maze. You don't need to book much in advance.

My only piece of advice is get the bus early enough to allow time at Tarifa. I almost didn't make the ferry as they took so darn long at the terminal processing the passengers, the ferry doesn't wait. They closed the gate and started to take off with about 40 of us in the terminal. After much protesting, the let us on. Going back was easier.

Hope others find this helpful. I think the cost was about 55 euros for one person. More people you can get a better price.