for me the local autocrosses cost $35 a day.
I havent looked at HPDE lately and someone who runs them can chime in, but IIRC its loke $200-$300 a day.
the thing that you have to keep in mind is that HPDE can give a few HOURS of seat time.
autocross usually affords several minutes of seat time
drag race only gives about a minute or 2 of total seat time for a given event. (if you take alot of passes)
i dont know what going to the strip costs (never done it) but if you count $ per minute behind the wheel in anger then HPDE is a big winner.
you can make ANYTHING involving cars expenisve, but it still is gonna cost a few $$$ to have fun.
additionally
Strip- you car is probly good to go, take or rent a helmet
Auto-x- car is good to go, may want alignment tweaks and tires, take or rent a helmet (my club has free loaners)
HPDE- upgrade your brake pads and probly take spares, helmet, and maybe a rollbar (convertable?)
btw, heres what I run,