I don't think there's one good answer, but I'll take a stab.
There was a time when you might have called nitro cars sportsman since they could affordably/profitably put on shows at small tracks without sponsors. When they made themselves too expensive (One good friend says it was when they figured out they could use a high speed leanout to make them go a little quicker/melt the pistons, requiring the tear downs after each run) for this, alcohol cars stepped in to take their place. When I started going to local bracket tracks in the early 80s, alcohol funnies were still occasionally booked in and paid to make three pass shows.
I guess the days are about up for anyone running unsponsored in either of the nitro classes, huh? Wasn't that long ago when you could see operations running nitro with lower annual budgets than people running for points in alcohol.
My numbers are old, but the last I heard a PSI blower for an alcohol car was going for $15,000 and titanium valvesprings were around a grand a set. Don't think carbon bodies and titanium trees are exactly free, either.
I think the main difference as far as NHRA is concerned is that pros get in free and sportsman still has to pay an entry fee. The entry fee almost seems a slap in the face for anything from comp up, or even for the budgets that some have in their super operations.