Hmm. If it looks too good to be true....
These two agencies claim to be able to offer a spectacularly large number of girls throughout the whole of the Netherlands and Belgium, "from 125 euro" regardless of location. However, none of the profiles gives any clue as to where the girl is based or availability. And look closer, and the starting price turns out to be higher than the "from 125" shown on their rates pages - "from 180" in one case, and "from 150" in the other. And the operative word here is "from" - most reputable agencies give actual rates. I suspect that when you contact them, there will be a very limited number of girls available in your area, and at considerably greater cost than you might be expecting. Many Netherlands agencies (such as that recommended by the previous poster) set a minimum booking duration of two or more hours if the girl has to travel any distance.
I have used the agency below (admittedly quite a few years ago), and their rates page shows their
actual prices for remote areas (rather than the hype "from 125" prices of the above two agencies):
External Link/Members OnlyCertainly try your luck with the two agencies you have found - nothing ventured, nothing gained. But I would suggest you contact them, before you go, and ask which of their girls cover the specific town that you will be staying in, and what the actual cost would be. You will be able to judge how legitimate they are from how vague or unrealistic their answers are.
And I would strongly recommend having a few plan Bs up your sleeve, such as doing a google search on agencies that specifically cover the Gelderland region.