Wow, the dirt bike market must really be in the toilet nowadays!
I'm w/ Hemibee, and after getting my first KTM after many Japanese bike, I now have 3 of them. Parts cost hasn't been an issue, b/c they so rarely need any other than oil filters for the 4 strokes. I did just have the fork seals replaced on the 300 (first time they've blown on any of my KTM's), and the fork seal kit was $29.95. I've also spent a lot less on mods since they come so well set up for woods riding.
I've found my KTM dirt bikes to be really easy to maintain. The 4 strokes are more work to change oil on than a CRF, but your intervals can be a good bit longer. Valve adjustments are super easy, so shims or feeler guages needed. The 300 is prob. the easiest to maintain bike I've ever owned! Seems like bolt sizes are more consistent, and they're easier to wrench on (i.e. seat comes off w/ one bolt). Don't forget, no linkage to lube (though I'd agree this is prob. a disadvantage for MX, but I'm pretty much retired from that). Both have been super reliable, and the 300 is prob. the best bike I've ever ridden off-road.
I have to admit that those CRFX and WR deals are pretty attractive - I'd prob. go w/ the Yamaha if I was in the market for a new 450.