You will need a server to run. Because one time installation isn’t a final spending. You have to buy a domain name, a hosting( preferably a KVM VPS) which means you cannot buy from any of the hosts giving OpenVz and LXC VPS.
You may have to spend atleast $10 for non recommended 1gb RAM host. So you may have to stretch you budget atleast $140 per year.
We hope you will run discourse soon.