I think that the CN option is the best one:
-It´s a cheap option 100000€ the complete pack, chassis with engine (1/4 of a lmp2 car), and the parts are cheaper than a Clio cup car
-The CN cars are capable to do a 6 hours race
-The CN constructors could go to the major LMP class easily
-You can feed the major classes with new drivers
-New teams
-There are a lot of chassis options
-It remember me the old C3/C-Junior times
...and much more