How much is the lowest price for iCloud storage only

The 5GB plan is free. The next plan is 50GB and prices vary by country. See: iCloud+ plans and pricing - Apple Support

Note that there is no additional charge for the extras that are included with the storage (e.g., iCloud Private Relay, etc) and no option for a cheaper storage plan without those extras.

It would depend on your location, but the first tier after free is 50GB and that is $0.99/month in the US.

50 GB is 0.99 USD.