From the top of my head:
£186 for the Eurotunnel. I know it's cheaper on the Ferry but it takes much longer and it's generally more hassle.
£190 for the hotel at Spa.
£150 to stay at the 'Ring.
£4-500 on fuel.
£125 on 'Ring laps.
£??? on beer/food money.
Then the cost of the Spa trackday.
Budget things breaking/Bongard fails. I had a £7k credit card with me 'just in case'.
My fuel was better than expected on the journey , though single figures were seen on the track ..
From the ring to the eurotunnel at Calais is approx 300 miles. , which is doable on a tank, even if you have to press on a bit to meet the crossing time
.
From Calais to spa is approx 212 miles , which. Is not a bad drive. Mostly motorway, extra costs for the recent trip were a stay over in Folkestone , though I don't think I'd do that again as it's only 120 odd miles to the tunnel , that did break the journey up a bit but not necessary if you're a short drive from the eurotunnel in Folkestone.
Accommodation is variable depending on where you stay , Two nights in the raddison blu , is what you want really , all you need and more. That is approx £75 per night which includes breakfast/wifi , this is the best hotel for a spa trip as it's about 9 miles from the circuit but is located where all the bars / food places are.
Then there's fuel for the track day.
beer / food costs which is around 100 Euro per day depending on how much you drink of course.
I would say £1k for a trackday trip to spa is about right.