yeah .3 mm is a common first overbore
you might be able to find an OEM or another aftermarket like SPI or Vertex that is a lot cheaper than wiseco.
i'll buy wiseco for something really nice and racey but usually i stick with the cheap ones... they made KE100's up until the early 00's so it shouldn't be too hard to find shit for them
i would say that if you have the choice to go with a plated bore vs. iron, you're probably money ahad grabbing the plated bore, especially if you plan on keeping it. You won't have to pay to have it bored/honed and it wont wear out as quickly. Plus if you get to the max oversize on an iron bore its junk... plated bores basically last forever and you just replace the cheap piston for this motorcycle stuff.