about racing In Thailand, it's up to mechanic experience, especially 4 stroke engine modified,
thailand have a lot race programmes/year and Race event continued more than 30 years ago; but only a few mechanic can be champion or the winner, so it's not mean only good luck for modified and be the winner.

Compare to cbr 125 modified 4 Valve DOHC or 2 Valve;
Honda Sonic 125 cc. like cbr125 but have some different parts.
mechanic started modified an raced Sonic 125 almost 10 years, so almost every case of modified and raced, Mechanic can made stable formular and best result for them,
each mechanic have own technic to be the winner, That's also called know how cost.
many mechanics can modified, as you can see in every raced Event,
but finally, you must believe from results.

expensive parts, we heard many jokes from mechanic experience with Imported part and our modified parts. as we confirmed compare cost/quality performance. Thailand specialized in this bike segments.
because mechanic already tested and raced all the time.

For cbr 150, only genuine part for DOHC system also high price, because a few units in market...

I not belief that parts for the Honda CBR150 are rare in Thailand, also I cannot understand why you write that there are only a few CBR-150 in the market... only this morning I saw 4 (in less then hour)

You should get yourself down to the track behind Seacon Square on a Sunday morning and chat to some of the guys who blast round there on their CBR150s. I'm sure they could give you a few ideas on how to modify one.