Mostly, you'll need experience regulating their environment. Temperature, humidity, and light cycles are all important to control when taking care of a reptile. Because, Cataphractus are sun-bathers, their environment is more complex to manage. They need heat and light available for long amounts of time, which means it takes care to keep a stable humidity and temp throughout each 24 hour cycle. They also need a complex habitat, usually involving sheet rock that they can both sun-bathe on and hide under depending on their preference. They also don't really like to be handled, and while it is okay to take them out once in a while, they require an owner with enough restraint to mostly leave them alone.

None of this is really that difficult, but requires patience and close observation - especially when dialing in the habitat's features. You can buy a few lizards that need a fairly specific climate and geography to get a feel for what you'll need to keep a picky reptile happy.

Much more than the experience or cost, the limiting factor to buying a true armadillo lizard is availability. There are tons of places selling relatives to the Cataphractus under the title of "armadillo lizard", but real Cataphractus are very few and very far between. They really can't be shipped long distance, which means that getting one relies heavily on someone within a reasonable radius having one that they want to sell. The odds aren't in your favor, to put it bluntly.

I've been looking for a few years and have yet to see any reasonable opportunities to buy one, but hopefully the bad luck doesn't extend beyond myself.