The EUV source is just todays most obvious barrier to success. Tomorrow it will be the reflective optics including the masks, mask inspection and cleaning, and then resists. The companies involved in all of those areas need R & D investment help as well. There are still many obstacles to high volume manufacturing with EUV. And ASML alone wouldn't have to buy all those companies. Intel, Samsung, and TSMC could help. At this point they should just spin off a new company called EUV Inc. and invite a few more big semi companies to join. But that might make it too easy to figure out how much money they are spending on EUV.
I don't know that ASML has the means or the desire for such a shopping spree. Buying Cymer is one thing; buying every major player essential to the EUV infrastructure? That seems a bit much.
It is interesting, though, that the place ASML choose to buy its way in is the area that is standing in EUV's way. Despite what ASML says about selling sources to other litho vendors, you wonder if they'll keep them all to themselves (assuming of course that the technology progresses to the point where throughput is suitable).
We seem to be transitioning from vertically integrated companies to a whole vertically integrated industry. Too much consolidation will cause problems in the future. Is this cabal of companies already too big to fail? As @resistion says, why not buy all of the other major players essential to the EUV infrastructure while you're at it?