It depends on a lot of things - it can be quite expensive or pretty cheap. I am lucky that it is pretty cheap in my case:
Track time: free or $50/day (by virtue of being an instructor)
Tires: about $80-100 per day. $1300 for a set of Michelin Pilot Sport Cup lasts me 15ish track days (my 997 is much kinder to tires and brakes than any BMW I have ever driven)
Pads: ~$60-80 per day. Again, the 997 is much kinder on brakes than front engine cars and a set of (expensive) Performance Friction pads will last almost two seasons
Accelerated maintenance (e.g., more frequent oil changes, brake fluid flushes, etc...) - hard to say. I do that stuff myself on the 997 and so it's just cost of consumables which isn't very high.
Hotel: $0 - $80 /night. Mid Ohio is a 55 minute drive from my house so I usually don't stay overnight but if I do, the hotels around Mid Ohio are cheap.
So my total costs now are probably $150-300 /day. But I remember when I lived in NYC and did track time as a student at Lime Rock with Hoosiers and a car that chewed through brakes where I was probably spending $1000+ per day easily.