The only way you will know how much the stakes you have in a bounty is when that bounty is over as there are many factors that will contribute to how much you can get. As it will be calculated to the allocation in a campaign, number of participants and how much money was put into the project of course if it had reached the hardcap it will be much highers or so on.
It looks like OP is interested to know how many coins he may get for this work on that campaign in advance means before he joins the bounty. But it is not possible to calculate in advance.
If the project didn't go on as per calculations many times you will get very less money for your work and this is risk people taking to join any bounty program.
