The cost to buy a Nepali passport on the black market is reported to be $1,740 (150,000 Nepali Rupee). If a legitimate visa is included with the fake passport, then the price rises to $6,961 (600,000 Rupees).
The passports are reportedly bought by Bangladeshi nationals who use it to increase their chances of obtain employment. In addition, drug traffickers and wildlife traffickers occasionally buy Nepali passports to hide their identity.
Source: “Nepal emerging as ‘regional hub for human trafficking’,” eKantipur.com, February 24, 2013.