Your cost are well within the norm for a EU vacation -$4-5k for two people. The trains are great but to really get around a car is a must, Dupont,Silly,Fantôme,Orval,Dubuisson,Achouffe are all out in the sticks.
Plus theres all these little places along the way >

That castle was just something we noticed while driving and decided to stop.
Another stumble upon, we decided to have lunch while looking over the landscape.>>
link
Now some badnews>>
Lastnite over dinner wife says the tickets for the F1 race will be around 900£

`about lost my appetite but as she explained its once-in-a-lifetime experience. More costs to come I'm sure
But this will mean we've covered the entire eastern/southeast of Belgium leaving only the coastal areas for another time.