looks like someone tried drilling the mast to arrest the cracking already. you need to pull the insert whcih is probably where your problems lie. when that's addressed, welding a band on the base probably would only cost a couple of hundred- if the crack progresses the price to fix it mounts.
Capt. Force's solution is a good one too (if there isnt too much taper to refit the step)
"Never attribute to malice that which can be adequately explained by stupidity." - Robert A.Heinlein