Do you really think the transaction cost has any risk of becoming "high" in the foreseeable future?
Nope, and transactions will probably never be "high" in cost. On the order of a penny or a couple of pennies.
On the other hand, the price for opening a new account (reserve of 200 XRP required) and creating / listing self issued currency pairs (50 XRP I believe) will be more substantial. It is not the cost of individual transactions that will make XRPs scarce but rather, the reserve requirements.