How much should I expect to pay for 1.25-inch black iron pipe?

I'm installing a Noritz tankless water heater with a heat output of 200k BTU/hr. Tables in the water heater's installation manual say I'll need to supply at least 200 cubic feet per hour of natural gas. A pipe run of about 155 feet will be required from the gas meter to the new water heater, and the tables indicate that I'll need 1.25-inch pipe for a 155-foot run capable of supplying 200 cubic feet per hour. Best price I've found so far is $5/ft for 1.25-inch iron pipe. Does all this sound reasonable, or am I mis-reading the tables and oversizing the pipe? The current pipe that delivers gas from the meter to the water heater's location is 3/4-inch, and it was adequate for a 55k BTU tanked heater. Is the $5/ft price as low as I'm going to find for 1.25-inch iron pipe, or where might I find lower prices? Thanks for your help!