Currently, the proposal fee is 25CRW.
This used to be around 25 to 50$. But is increasing rapidly.
The goal as far as I understand for the fee, is to incentive quality projects and keep spam away. To avoid a Dash situation where one has to pay upwards of 1k for a proposal, why not decide what a reasonable amount is, and make a fixed function for that.
Keep the fee in escrow until superblock is reached, and then release the fee back to all the proposals that passed.