Doesn't matter how you limit it. The fact remains that you're still claiming that activities (not all activities, necessarily) which are not interstate commerce in themselves, yet have an effect on interstate commerce, can come under the control of Congress, despite the fact that the language of the Constitution doesn't authorize it.
There is no requirement, nor is there any justification to artificially dissembling the market into local and regional parts.
There's nothing artificial about it. All that needs to be determined is the nature of the transaction. If it's interstate in nature (that is, involves exporting an item from one state and importing it into another) then it falls under the regulation of Congress. Otherwise it doesn't. All other considerations, such as whether we're dealing with a market that's "interstate in scope", are truly artificial alterations to the language of the constitutional grant of power.
The limits are defined by the market itself.
"the nature of the transaction."
The nature of any particular transaction is irrelevant. The nature of the market is what determines applicability.
""interstate in scope", are truly artificial alterations to the language of the constitutional grant of power."
No. Refer to creation of the shoe monopoly and the various other private actions that provided motivations for the Constitutional Convention itself. Also review the quote from Madison you posted noting that the intent there was to remove State power to favor their own players over those of another State. That intent is contained in the purpose to provide market fairness and equity. That applies to the players, the people. The States were removed from the getgo.