There are three schools of thought, and they're all right. Ask for ERW (Electric resistance welded) or DOM (Drawn over mandrel) or 4130 Chrome-molybdenum tube.
They are all structural tubes, defined by an O.D. and wall thickness. Pipe is defined by I.D. and pressure rating ( 2-inch Schedule 80, etc.)
ERW is commonly used for building tube structures, and is the cheapest of the three. DOM is more exact in the ID and OD, and is used as hydraulic and pneumatic cylinders. 4130 and its cousin 4140 are high-strength alloys that are used in critical applications like race car frames and aircraft and are the only tubes commonly available in sizes that will telescope.
The conventional wisdom is that DOM is a little stronger, but also a little more brittle, and will break in cases where ERW will bend. 4130 is stronger still, but best left to professionals since it requires special welding techniques to maintain its strength.
Personally, I recommend ERW for your application. It's easy to work with and plenty strong.
I'm sure there must be a suppler in the Omaha area, but if you can't find one, call my supplier in St. Louis at 800 833-1259 or go to their website, Shapiro Supply - HOME
. They ship all over the country and have good prices. Tell them that Jim at B. Dash told you to call and you might get a break.