"However, I wonder if it's worth to spend $400 every 5k miles on a bike that is worth $2000."
thus the DIY suggestion was made
agree newgen (shims) frequency is 7500, not sure, but i beleive the OP's (@Thouse) pregen (screw and locknut) is 6000.
I'll contend doing a screw and locknut valve adjust is really not bad at all. Just take your time. And don't blow it off!
https://faq.ninja250.org/wiki/Do_I_r..._6000_miles%3F
a quote taken from the above link: That is why probably fewer than half of the Ninja 250s sold
ever get their valves adjusted.