Is there an open-source / free official Myers-Briggs assessment I can adopt? Background

I've got an idea for a web site that uses one's Myers-Briggs type as part of the value. 

I've seen various web sites offer "quick quizzes" to assess one's MBTI, but I'm not sure how legitimate / effective / ethical it would be to utilize one of these "knock-off" assessment techniques. I haven't decided any of the business angles yet; for now it's just a cool idea, so I can't speak to whether it would be commercial, non-profit, etc.

Questions


Is there an official "test of record" or set of questions that I can use in my application that is reasonably open or inexpensive? I'd like to get results that are as accurate as possible but I'm just one guy on a shoestring budget.
Could I run into legal trouble from the Myers-Briggs institute over this? How open are they with the methodology for this assessment? While I'm strapped for cash, I also have no desire to be a jerk; I'm admittedly ignorant on how this realm of science/industry views these matters.
Is there any need for an official MBTI interpreter (other than privacy ethics, etc. which of course I would be respecting as the founder of said web site)? 
How much accuracy does one lose in using a quiz that isn't "personally reviewed"? That seems to be the main purpose of a "licensed MBTI interpreter" as far as I've been able to see with some quick research.
The IPIP may provide what you are looking for.


  This IPIP Website is intended to provide rapid access to measures of
  individual differences, all in the public domain, to be developed
  conjointly among scientists worldwide.


In general, the scientific literature tends to focus more on a dimensional approach based on the Big 5 model of personality than the type approach. There are strong correlations between MBTI and Big 5 measures. 

The IPIP website provides measures of the Big 5. The following table from Furnham (1996) summarises some correlations across a few studies between the NEO Big 5 and the MBTI.



You can find a listing of some of the multi-construct measures including Big 5 measures on the ipip website.

References


Furnham, A. (1996). The big five versus the big four: the relationship between the Myers-Briggs Type Indicator (MBTI) and NEO-PI five factor model of personality. Personality and Individual Differences, 21, 303-307.