It's only fraudulant if you don't report it. And you should charge the highest possible sum you can, IMO, or whatever sum you choose if you're being charitable. In such a hypothetical case - it's your project and so the upper limit is the value you place on your own time and energy. Also, since it's OSS anyway, there is no price set to compete against.

Part of the point of setting a high bar would be to either:

1) receive adequate compensation or 2) get the company that can't afford to pay you to contribute in some other manner