Even if you already own a Vanagon—or if GoWesty were to give you one for free—the cost to go through it from end to end just mechanically is at least $25,000. Folks bring them to us all the time, from all over the country, and when we are done the bill is usually between $30K-$60K. This may seem like a lot of money, but compared to "fixing it up as you go along," it is actually a bargain.
For instance, we commonly get stacks of service records with the Vanagons we buy to fix up and re-sell. Going through the records, it is common to find that people have spent $10K-25K over the years, basically wasting money and being terribly inconvenienced. It is typical to see an invoice ten years back for a fresh engine, two hoses, materials and labor, total: $5000. Then two years after that, another invoice for a fresh engine, two other hoses, materials and labor, total: $6000. Then, four years after that, ANOTHER fresh engine, a radiator, materials and labor, and another bill for $6000. All that money wasted on redundant repairs just for the vehicle to end up in our hands for $3500, with another blown engine. We see this sort of thing all the time, and it is just pathetic. Some people deduce that these vehicles are just "not very reliable" or even downright "possessed"—as though they have gremlins just waiting to ruin the unsuspecting driver's day. That is just not the case. Any 20+-year-old vehicle will only be as reliable as the least reliable part. And, the failure of even one $3 coolant hose can take out a fresh $5000 engine—we see it happen all the time.
These vehicles do not get "possessed" or anything of the like. Unfortunately, that is a common perspective from many mechanics that just fail to grasp the age of these vehicles and the need to approach each system—and, in fact, the vehicle as a whole—in a holistic manner. Most shops approach the repair and maintenance of a Vanagon in the same way they would fix a five-year-old Toyota. That just does not work, given the age of these VW campers. It is not a "VW thing," or a "Vanagon thing"—it is an age thing. That 5-year-old Toyota would require the same approach that GoWesty takes… twenty years down the road. The reason you don’t see the same effort put into 20+-year-old Toyotas that you see people put into Vanagons is simple: they rarely become "part of the family" like your Vanagon, with all the memories and emotional attachments that come from such a relationship. When a run of the mill Toyota starts exhibiting "bad" behavior due to age, they usually go straight to the crusher, no emotions attached.
The cost to restore a Vanagon just to be reliable and safe so it can be used on a daily basis— and not nickel and dime, and five and twenty you to death—is the same whether it has a pop-top or not. There are lots of other, way more modern and safe vans without pop-tops that you can buy for less than what it costs to restore a Vanagon. For instance, a later VW Eurovan, or even a Honda, Toyota, or Nissan. They are not as cool or fun to drive as a Vanagon, but they get the job done, are easy to find, and can often be financed. The only thing that makes restoring an older VW Vanagon remotely sensible is its uniqueness with respect to its pop-top feature, fun and enjoyment notwithstanding. So, if you desire to own a Vanagon because you think it will be cheaper than one of the other vehicles I mention above, think again. Sure, it is possible to go out and find a Vanagon for next to nothing, or you may already own one that is "due" for a restoration. But unless you are a mechanic and enjoy working on your own vehicle, I would not recommend trying to own one "on the cheap." It will lead to disappointment, frustration, and even possible bodily injury.
My advice is this: if you already own a Vanagon and want it to be reliable and safe, you need to budget at least $30K to have it thoroughly gone through by a shop that understands these vehicles and approaches the task with a holistic, system-based mindset. If you don't already own one, you need to add that to the cost of the model you desire, which can vary from $0 to $30K, depending on the year and model.
Do it once, cry once, be done with it, and then just enjoy life. That is the best advice I can give you. Really.