When I started in construction at age {18} I worked for a man in NY who installed underground gasoline storage tanks at gas stations.
All the suction and vent lines from the tanks to the gas pumps were threaded galvanized {or maybe black iron, I cannot remember}. The largest pipe size we used was 4". So we were cutting and threading pipe sizes 2" through 4". He taught me that the correct wrench for 2" pipe was 24"; the correct wrench for 3" pipe was 36" & the correct wrench for 4" pipe was 48". And he had all those size wrenches.
As a skinny 18 yr. old I was trying to keep up with the men using the 48" wrench. If any of you have ever tried to screw a whole length of 4" steel pipe into a threaded fitting, you know it is not easy to get it started...LOL. That pipe has to be lined up exactly to get the thread started and it is heavy to hold it by hand while doing that.
Anyway, I would check garage sales. You may just find an old rusty wrench that just needs the rust knocked off.