Trackdays generally cast between anywhere £69 (half day) upto £400 full day premium dates

Expect the average cost to be £150 for a full day.

Fuel can be 1 full tank per day (not including getting there and back) so budget £55 for that, then your normal travelling costs.

Tyres - spend what you like really £250 should see you in the cheap get you going part of the market.

Brake pads £80 - £150 (should last 1 year)

Brake Fluid £40 (change TWICE a year)

Safety items like helmet, harnesses, etc spend what you can afford to get decent stuff.

HTH as a starter