A tariff is a species of tonlieu. It is a fee collected by the sovereign of a territory in exchange for the privilege of transacting business within his domains. Some markets are more rewarding to merchants than others, either because of their prosperity or their lawfulness or their just laws – or all three, for prosperity is correlated to lawfulness and just laws. The more rewarding a market, the more a merchant ought to be willing to pay to play in it, and the higher its tariffs should be.
A sovereign interested in maximizing the net present value of his revenues, then – as all sovereigns ought to be (and are, whether they admit to it or not) – would do what he could to ensure that his laws were just, and that his subjects were lawful and prosperous.
Even when they truly serve the common good, laws can be unjust on account of their inefficiency – of, e.g., their complexity, incoherence, difficulty of administration, cost of compliance, and so forth. So the sagacious sovereign would try to make his laws simple, easy to understand, consistent, and easy to follow. This would generally mean keeping them few, and minimally invasive.
But how then should he decide the proper tariff? By increasing his tariffs on all merchants until he sees the increase in revenues generated by the marginal increase in tariffs going to zero. This would subject the most successful enterprises in his domain to appropriate foreign competition, while preventing it from cutting the legs out from under the most vulnerable of his subjects.
Likewise for tolls on visas, another form of tonlieu. These too ought to be set as high as can be without reducing their increase of sovereign revenues to zero. They ought furthermore to be strictly limited as to duration. Renew your visa as you like, but plan on paying just as much to renew your visa as you paid to get it in the first place a month ago.
As for tolls and tariffs, so a fortiori for the price of citizenship.
It ought in justice to be more expensive to get into America than anywhere else in the world.