madduke I think this depends very heavily on your overall financial situation, and how much value you're getting out of GrapheneOS.
I think a good question to ask yourself is "how much would I pay for the ability to use GrapheneOS if it wasn't free?" and go from there.
This isn't specific to GrapheneOS, but it seems that people always assume that free software will always be there, and that it will always remain free no matter whether you support it or not.
The reality is that a project of this magnitude needs people to work on it, and to do so constantly, especially in the context of Android's fast-moving environment.
That is to say, if (for example) a free email app needs support for development to continue, you need to multiply that by a lot for a project like GrapheneOS, because the amount of work that has to be done is that much more.