Another avenue to consider is BMW club racing. At least you won't have to drive a Miata.
BMWCCA has similar 13/13 rules to the Porsche clubs, and there are Stock and Prepared classes where the cars are semi-street drivable. That means you can probably drive it to the races, but you won't want to daily drive it. A guy with a SpecE30 with slightly bigger tires and a chip has turned 1:37 laps at Big Willow. If it were prepped to the limit of BMW Prepared or even Stock rules, it would be faster yet.
You can start with a $1000 e30 or an M3, with everything in between.