Starting with the most Dutch question: what did it cost? And how did we budget beforehand?
I would suggest to:
As one of the first things we sat down and determined our camper requirements and a spending limit. We answered questions for ourselves like:
For us we decided we wanted manually pumped water (cold only), no bathroom, no real heating, plenty solar panels, no inverter, something for bikes, an awning, a two-burner stove, etc. The van should be just big enough to stand in upright and lie down in stretched out.
Then we looked at how much money we could pump into this and how much a van conversion should cost according to other blogs online. In the end we set a limit of €20'000, that would be the absolute max for everything (vehicle + conversion).
Then we started to make a detailed budget, i.e. a breakdown of all the expected costs. I found this difficult, as on the one hand you want to be realistic but on the other you cannot actually make full design choices yet. For example, a lithium battery is much more expensive than an AGM one, but you couldn't really know what you need at this point. For most of it we did a combination of reading other stories and browsing online for parts to buy, feeling out an estimate of prices.
The sum of the budget should of course be less than the spending limit. Don't be afraid to iterate at this point: if you exceed the limit, reconsider if you need to lower your expectations (change requirements) or simply put aside more money.
Our full budget is in the next section, together with the actual spending.
Below is the complete budget and the realized spending for our van. Note that I cheat a little here, when I made the budget before building we had different (and impractical) categories, so I rearranged the entries without changing the meaning.
The total cost in the end was pretty close to the budget we made, though not each category individually. We were hoping for less in total, but we did a decent job at the projection. The lines in grey we didn't include at first at all, but we did run into expenses that should have been in a budgeted category.
The sum of all money spent is accurate, we did write down every singly purchase. But their organization into categories is flawed, especially for the many runs to the hardware store when we bought lots of materials for different purposes at once.
Some notes I want to add on our spending / budget: