No. I'm not sure of the figure of 'bona-fide' Hi-So Thais (whatever bona-fide would be). It's a guess by me, but good idea, maybe AI would have a better guess.
By wealth - some of the aristocracy "Na-this, N-that" surnames) are not wealthy, because the name comes from history and historic wealth, and in some cases, that wealth has already been tapped out or frittered away by former uncles, aunts, whatever. So you can't necessarily tell by a 'sakinda' name. Still, many are well-educated even if not wealthy, and have a decent home, and the family name still opens doors - and they know 'extinctively' who they will and won't vote for. The pee-noi system though extends through society and in the upper wealth category the extended families can be quite big, and the patron dishes out the cash via the old Chinese guangxi-type of distribution - or other ways if not Thai-Chinese but still very wealthy. So ultimately it's probably a lot larger than 500 - a guess at the number of ultimate family heads - bigger number is probably in the low thousands - but in a country of 70 million, with the majority earning minimum wage USD 10 daily, or even twice minimun wage, it's still working poverty in comparison to the well-connected, many of the latter scared of the majority with a vote.