As freelancers will compete by submitting hundreds of ideas when they join your contest, the prize should be funded when you start it to gain the confidence of as many freelancers as possible.
Once the contest is posted, you can no longer reduce the prize and change the currency. So make sure to double check it before clicking Get Entries Now on the Start a Contest page. You can, however, increase the prize money while the contest is open. Funds will be taken from your available Freelancer.com account balance or your verified payment method if your balance is insufficient.
You can award multiple winners, but the contest prize cannot be divided among them. You will have to fund the prize for each additional winner.
The prize will be released to the winner after you accept the submitted files on contest handover.