From that site you posted, it looks like Dr. Stacpoole is going to see if NTBC works to reduce side effects of DCA. NTBC is also called Orfadin. (I had to look all this up)
http://groups.msn.com/tyrosinemia/ntbc.msnw says "The drug's cost depends on the dose, which varies with the child's size: $12,000 a year for an infant, up to $60,000 a year for an older child, estimated Bo Allen, vice president of Orfadin's manufacturer, Rare Disease Therapeutics. "
This drug was approved under the Orphan Drug Act, and those drugs are usually very costly.