If you want to do 3-4 laps then buy a 4 lap ticket which is about 100 euro.
Spend as much as you like on food/drink. I reckon if you allocate enough to fill the car 4 or 5 times in total, you'll be about right (2 of these in Belgium on the out/return trip). If you get short of cash there's a cashpoint 5 mins up the road from the hotel where you can get more euros out.
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