Just because I still think about it sometimes, here are the spot prices today for single static IP addresses (based on a 30 day month):
April 22, 2021
Azure - East US
Google - Iowa
|In Use (Standard VM):||$2.88/month|
|In Use (Preemptible VM):||$1.44/month||Not in Use:||$7.20/month|
Amazon - US West N. California
|First, In Use:||$0/month|
That's it. Not a lot of price movement in the last 18 months. Azure has tweaked their Standard ARM up a little, but has removed it's penalties for additional IP addresses above 5 in other categories.
Google now allows you to select by region, but the region prices are the same.