We expect that post-singularity there will still be limited resources in the form of available computational resources until heat death.
Those resources do not necessarily need to be allocated fairly. In fact, I would guess that if they were allocated unfairly the most like beneficiaries would be those people that helped contribute to the creation of a friendly AI.
Now for some open questions:
What probability distribution of extra resources do you expect with respect to various possible contributions to the creation of friendly AI?
Would donating to the SIAI suffice for acquiring these extra resources?
You're getting into basilisk territory here. It probably makes no difference, at least at this point in time, when nobody has any clue what the most probable superintelligences will look like, and what their exact policies will be on this sort of thing. Although I guess we can assume that a superintelligence will use whatever policy has the highest likelihood of making itself come into existence, which as far as I can tell, is not necessarily the same as whatever policy has the highest likelihood of getting you to contribute to its creation.
Be thankful for that and pre-commit to always refuse extortion, before anyone does figure this out.