Depending on the distance that you want to ride (usually varying from 50km to 250km) the amount of money that you pay is fixed and varies between fl. 4.00 and 7.00 Dutch guilders. In that amount is insurance included. You can ride in one of the groups that most often is formed spontaneously, or ride in your own pace.
When you prefer to go your own way, a good suggestion is to ride the 'Tour d'Auberge', a tour of 13 stages (max. but you can combine stages) along Youth Herbergs (modern) where you can spend the nights and have meals at affordable prices. Cycling this Tour will show you all different areas of The Netherlands and you will see more variation than you would expect. Especially the Limburg region (where the professional Amstel Gold Race is being held) has some very steep but short climbs. Unfortunately, the route desciption that I have is in Dutch but you could write the NJHC if there is an English version.
The mailing address of the above mentioned organizations: