Street car racer here, $4,000 is the beginning of your troubles. I'm dropping $1,000 on new tires tomorrow (I got to
this level of wear in less than 9 months, and I only drift occasionally. Drifting frequently will eat your racing tires up in just a month or two). I just dropped $400 on new rotors and $300 on new brake pads last week (also got burnt out in the same time frame). Your Miata will probably come with an open differential which is useless for drifting, you're gonna have to upgrade to a limited slip differential which will run you $400 (
ebay) plus labor, that one's gonna be hard to do in your garage. Since you'll be drifting you probably will want to increase your final drive ratio to increase power in lower gears since the Miata's light on power to begin with too, no idea how much that'll run you but you can swap that out when you're doing the differential swap probably for no labor cost.
As you get more into drifting you'll need to get a roll cage to stiffen up the chassis of the car, miatas flex a lot and flexing will forget your stuff up drifting. You're gonna want to get racing bucket seats because it's very jarring to get thrown around when you're drifting, those are over a thousand dollars a pop.
Not to squash your dreams or anything, but the price of the car is just the beginning.
