I keep every receipt because being cheap I want to know so I can always evaluate if it's worth it.
The car after 30 years has $8800 in it, this may go down as I sell off some more stuff but not by much.
I have a $7,000 camper van (cheap motel on wheels) with a $500 trailer. We've both of these for over a decade.
My built up motor that went kablamo cost me $92 per event, I use one set of tires per year (two vintage race weekends and 4 track days) at $886 per set. Gassing up the van sets me back $375 - $390 per year depending on the price of gas. Race gas for the Datsun runs me $240. Entry fees for the vintage events are $975 (instructing at track days covers the entry). As I'm only doing 6 events a year my futile replacement costs are really cheap; the motor only holds 3 1/2 quarts and the tranny uses 1.2 liters. $39 last year.
So one the average year I'm spending $3000 - $3200 per season on the Datsun. I run local events (the track is 60 miles from my house) so that obviously cuts down the costs. I have calculate the extra expense for out of town events and the van would swallow another $120-$150 in gasoline.
If I amortize the cost of the van and trailer plus consumalbles that adds $785 per season.
Amortizing the cost of the Datsun is a little more discuss because from 89 - 91 is was an autocross car while we were converting it to a road race car. Then in 96 & 97 I ran the Showroom Stock Miata, I only did one or two events with the those two years. Then from in 98 I sold it only to get it back in 2003. So I've actually only run the car for something like 20 seasons. So I'll call that $450 per season for the car.
For just the Datsun I'm spending $4500 per year if we calculate the cost of the car and tow vehicle.
Now throw in the F500 I autocross; I've had it 4 years and have $4000 in it (it's actually $3986) and I've purchased two sets of tires (it came with a fresh set) so I'm spending $750 a season. I do 6-8 events a year with it. Max spend on entry fees are $240, I use 16 gallons of fuel $115 (uses pre-mix). The autocross site is 9 mile from my house so the van needs $6 in gas so right on $50 per year. All in I'm at $2,100 to $2,200 per season for autocross (I could a more exact number if I went to the garage and got the receipt book). So autocross is racer pricey for seat time but we all knew that.
So if we add my autocross and track events I'm spending $6,000 to $6,800 every year.
It hasn't been until recently (last 6-7 years) that I could afford to spend this amount. For many many years my anual budget was $3,000. I bought used tires, had a more Miley tuned motor (it did 62 races) and used the stock 4 speed gearbox.
If I really want to go total low budget for vintage races I'd go with a 1.6 Miata, drive to events. I'd leave the house at 4 A.M. Saturday for out of town events and only get a room on Saturday night. You could also run used race tires or 200 tread wear to stretch the budget even more. Doing that would make it possible for me to do 5-7 events for about $1800 -$2100 a year. We have an NA Miata that is now a spare car that's got Spec Miata suspension on it so I'd just need a cage (I have an extra race seat) and belts. We'd have $3,800 in it race prepped as we only have 3K in the car.
With all of the above said the one thing to remember is I'm running between 5th to 9th overall in the Datsun (depending on the group I get put in) out of groups of 18 to 25 cars. I'm a better than average driver so that helps, an average driver would probably be 9th to 15th with the car.
You can go racing for stupid cheap if you don't care where you finish or what you drive. The trick for me is I've never owned a new car. The most I've ever spent is 17K for the 2011 Outback I purchased 4 years ago.