I don't understand why you state a large cost differential between RCBS and other mfrs' dies, unless your AI caliber is the reason. In standard dies, they're all (except Forster) usually within a couple of dollars of one another. I would have suggested Forster for your caliber, but they don't have the AI die.
The difference is in the type of seater. Forster and Redding's Competition dies use an alignment sleeve that greatly improves run-out reduction; the Hornady seater has a compromised version of that. Redding's standard and everyone else's dies lack the feature.
You apparently aren't giving consideration to a bushing-style sizing die. If you were, the Redding Type-S set would be a good choice, but you're paying for a micrometer seater to get the alignment sleeve feature.
If I were in your position, I'd contact Forster and see if their std. seater will work for the AI, and then choose someone's sizer to pair with it.