Very interesting question posted, there is no one answer unfortunately.
Building a competitive race car, in any series, depends on the class and series rules as to how much it costs to run at the sharp end. Given you can drive at the sharp end.
I don't think the build and preparation costs of Spec Miata and Spec 944 will be that different. We haven't built a Spec Miata (yet) but are completing our third Spec 944 this year. The costs discussed for the build and prep on most of the posts are B. S. Yes you can buy or build a 944 for 10-12K but it won't get you a reliable AND competitive car. The cost savings for the spec classes is in reduced component cost due to the rules restrictions for that class (stock brakes, Toyos that last a few weekends vs. Hoosiers that last for one etc.). The big advantage for the spec classes is that it is not nessessarily the size of your wallet that will determine the race.
As for which series you run, where and when do you want to race? we race in
PCA because it provides a great opportunity to travel to great tracks and meet and compete against people from around North America. We have made many friends doing this. If you want to race more frequently and perhaps not travel so much then SCCA and NASA provide regional series to accomplish this. The advantage of
PCA and some NASA classes is the 13/13 rule. This rule eliminates contact as a race strategy and greatly reduces operational expenses and risk. We all go back to work on Monday.
The Spec 944 can be run in both
PCA and NASA now. We think this is a positive thing and will contribute to the growth of the class over the next few years. With that in mind, MantisSport is preparing two cars for rental to customers wanting to try racing or try the class. We have plans to prepare more when and if demand warrants. We think they are a relatively inexpensive car to build and maintain and, with rules stability, will continue to be competitive assets for some time. Our forecasted operating costs are a fraction of our little yellow Cayman S which competes in
PCA stock D class. If they get 5+ cars out on the track it will be very competitive racing compared to
PCA stock classes which require considerable investment to run at the front.
Having said all of this, racing cost money. More money to win. Pick the car and series that suits your budget and aspirations. Do you like to build? Do you like to drive? How much set-up and tinkering do you want to do? Where do you want to race and how much time do you have to race. There is a place for everthing and everyone out there.
Have Fun;
Stan