I recently installed my 10' BUD on a 3" ID pipe (which is the conventional way to measure pipe). The OD was ~3 1/2" and would be what you-all are talking about. Tubing and Conduit are measured a little differently and I won't go into that here. If it fits your mount, then you only have to worry about the wall thickness to resist twisting in strong winds.
When I tried to puirchase a 10-12 ft length, I was told it would be about $8/ft and for my purpose I should look for some used. I eventually found a 9'6" length in a scrap yard for $20 and welded a couple feet of rebar on the bottom to get my dish a couple more feet off the ground. Once it is in the cured concrete, the dish and wind don't need to know that the pipe doesn't actually reach the bottom of the hole.
If Ihad used conduit of a lesser wall thickness, I was considering filling it with conrete also.
Just my thoughts and ideas FWIW!!
Steve