Greetings,

Go with black pipe + a screw on floor flange to embed in the concrete
for less than the cost of galvanized. If you want to get fancy you can
probably even rig it so that you could unscrew the poles from the tires
(bolt the floor flange to a cement filled tire instead of simply
embedding it -- or embed it with bolts during the pour and grease the
pole for easy removal.)

Special notes:
a) often pipe is coated with oils which may adversely effect
steel-cement bonding
b) black pipe rusts quicker than galvanized

Hope this helps,
William