They are still plentiful and great... Last I checked any 1000 that is commonly used can be bought for $900-$2500.
Other than hornets what else can you race for that kind of price. Not mention if you can purchase just the engine without the harness and injection its cheaper yet. While working with Engler I've had the same injection components and ignition on 3 different generations of YFZ engines with very little change.
Before we ran alky we had a stock r1 last for 76 races and we retired it. It won a championship that year in the 1x car. It was also still strong! And wait it ran on gas!

The Japanese engines with stock chrome cylinders, with stock internals, ran at the manufactures suggested rpm will last.
As mark says "PERIOD"
Like anything there's always lemons but they are uncommon.

I know fuel is a completely different argument and we will never be able to get guys to go stock on gas because of the safety aspect.