Hallo Lilly,

billig(er) wird die Platzreservierung fast nie (in Polen ist sie aber z.B. fast umsonst, in Großbritannien tatsächlich umsonst), aber in vielen Fällen ist sie deutlich teurer (de facto eigentlich Zuschläge).

Aber um zu sagen, wie das im Einzelfall ist, bräuchte man natürlich eine konkrete Strecke.

Viele Grüße, Hektor. 

In several countries here is simply not anymore the way to RES apart from a normal ticket-all tix sold are incl. a seat RES-other as DB, but like in airplanes. So you cannot compare all. As aobe: notably the hi-spped trains €* and TGV in FR are extra-priced, even more that go over borders, and others are as such not overpriced but extremely hard to get.

I don't exactly understand your question.  Can you please give an example?

When you use a pass it is your ticket to travel but some trains require a reservation as well, whilst some others have the option to reserve a seat.These both have varying charges depending on the operator’s charge and any booking fees the reserving agency charges. 

These reservations are always additional to your pass and, when required, you need to show both your validated pass and a copy of the reservation to the inspector. (In most cases this can be either the pdf or a printed copy, but in some instances a printed copy will be needed)