Actually, the alternative is not a gas pipeline, but a gas-to-liquids plant in Iran with the liquids shipped to India.
If I understand this correctly the amount of gas to be transported is 2.5 Million Tons/year. If my math is correct, this is equivalent to 450MMSCFD (million standard cubic feet per day). At current prices, 1MMSCFD is worth ~$5000, so the amount of energy has a current value of approximately $850 Million. Since the Iranians are offering this at 1/2 price, this would cost us approximately $450MM.
The capital cost, if I understand correctly is around $1 billion, with an annual transit fee to Pakistan of around $500 million. Adding the transit cost, the cost to us would be comparable to the international prices.
Compare this with a GTL plant built with Sasol's technology.
The company claims a single module or the Sasol Slurry Phase Distillate plant, that converts 100 MMscfd (110 terajoules per day of gas) of natural gas into 10 000 barrels a day of liquid transport fuels, that can be built at a capital cost of about US$250 million. This cost equates to a cost per daily barrel of capacity of about US$25 000 including utilities, off-site facilities and infrastructure units.  If priced at US$0.50/MMBtu, the gas amounts to a feedstock cost of US$5 per barrel of product. The fixed and variable operating costs (including labour, maintenance and catalyst) are estimated at a further US$5 per barrel of product, thereby resulting in a direct cash cost of production of about US$10 a barrel (excluding depreciation). These costs should however be compared with independent assessments.
In other words, for 450MMSCFD, the capital cost would be around $1 billion. The plant would produce approximately 45,000 bpd of liquids. The cost of converting the gas to liquid is around $5/barrel, plus the cost of gas and transportation. At these sizes, I'd say that we can make a very good case for a wholly owned Indian GTL plant in Iran with Indian ships running back and forth.
This would have the additional advantage of helping India develop and implement the technology that will be crucial for world energy markets in the coming years.
This can be a compelling BRM article. First of all, I need confirmation of the annual quantity, and investment cost of the proposed pipeline through Pakistan.