Most common types of stainless are non magnetic.
Most high strength steels, low or high alloy, are magnetic.

There are non magnetic high strength alloys, but I fear those have special pricetags too. No, for magnet bearing parts, the thinner the gap between the floor of the arena and the magnet, the better.
Any non magnetic material is fine for the job.Polycarbonate, HDPE, ali, Ti, brass and so on.

Point is, normal stainless is perfectly weldable to hardox.
That is why the bottoms of Satanix's wedges are made from 1mm stainless, with magnets cast in epoxy to get the result.