A set of new steps will cost you around $300. I don't know how long the original steps were warrantied, but you might find that information in your owner's packet. I recall seeing an "instruction sheet" in mine with a warranty statement on the back.
Trekwood has replacements for sale. Here's the link to the 9" rise triple step:
http://www.trekwood.com/products/277...us-Step-9-Rise Remember that there are several different "rise heights" so measure yours if you do decide to buy new steps.
I'd suggest you drill out the rivets, pull that step off, take it to a welder and have him weld/rebuild the cracked area. Ask him to beef up both sides while it's off the trailer. When you reinstall it, use stainless steel bolts, washers and nylock nuts in place of the rivets you drilled out. That way, if it ever happens again, you can disassemble it with just a couple of wrenches.
Using a step stabilizer is a "hassle" but it does a great job of stabilizing the steps and protecting them from collapsing under a heavy load.
Good Luck.