Wild Camping is officially forbidden in Belgium.
Bivakzones / Paallkampeerterrein:
These are small free camping grounds dedicated for hikers and cyclists. Currently there are 38 of them in Belgium. You can find their locations in a good hiking or cycling guide.
Some nature parks but also regular camping grounds have cozy log cabins to rent. Generally they are for 4 people and cost around 40-50€ per night in total. The dutch word for it is “Trekkershut”.
Belgium has a wide variety of camping grounds to offer.
Basic camping grounds cost approx 7-10€ per person when traveling with a tent. Off-season it might be cheaper.
Travelers with a caravan or camper will generally have to pay about 15-30€ per night for 2 persons.