I would recommend starting with Audio CD's available through people like Amazon or ebay at a discount. Books are a little problematic because you can't get a good feel for the tones and basic sentence structure so for book study to be successful you really need a teacher or tutor as well. For your situation I would recommend to start with the Pimsleur 4 compact disc series which retails for $19.95 but can be bought on ebay for $10-$15. You can listen to these and practice basic sentences at home or in your car. If this method of learning works well for you, then you can go on to the Pimsleur 1,11,111 series and then to more advanced courses after that from other publishers. Pimsleur will give you the basics.
If you are in business, I would recommend a dvd series like the business course offered by Sinolingua after you grasp the basics with Pimsleur.
All depends on how much you want to learn how fast and what is your final goal. I learned all of my Spoken, Reading, and Written Mandarin through independent CD/DVD courses. It can be done and eventually you will find what takes the most time is building basic foundations such as a fair amount of characters and vocabulary as Mandarin has far more words to express an idea than you will find in English.
Originally I only thought I wanted to learn to speak the language to get by, but in time realized that by learning to read and write allowed me an insight to the amazing Chinese soul.
I would also recommend that you invest in Pleco fairly early on.
http://www.pleco.com/index.html
This electronic dictionary will allow you to set up flashcards in many different ways that best suit your needs to increase your vocabulary. You will also be able to translate SMS messages you get on your phone in China as well as other documents.
This should at least get you started.