More/less just like budget required to run Bitcoin full nodes. You can run Bitcoin full nodes + electrum server on Raspberry Pi 3.
I've no idea about cloudflare integration, but there are many ways to protect server from DDoS attack such as block known malicious IP and limit request amount.
My raspberry is currently broken so my plan is to run it in AWS or DO with their free credit.
Well, I don't have much knowledge of other software only Cloudflare that I know to use to protect it from DDoS attack.
Bitmaxz, is cloudflare capable of that?
I don't know but it might be possible?
Temporarily I'm using https//coinb.in for making transaction from electrum offline and get hex then broadcast it to coinb.in just to make a transaction.