Brewer's: Lac of Rupees
The nominal value of the Indian rupee is 2s., and a lac means 100,000. At this estimate, a lac of rupees = 200,000s. or 10,000. Its present value varies according to the market value of silver. In 1894 between 13 and 14 pence.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894