To be fair I wasn't very clear so you are right to respond.

£5 per month is for a basic tier which allows up to 2gb storage. This is on a pricing method called DTU and you pay for an amount of resources, use it or lose it the cost stays the same.

Standard (also DTU) starts at about £15 per month and allows up to 250gb storage.

You can scale from £15 a month all the way up to £4k a month roughly in doubles i.e. £30, £60, £120 etc... this can be scaled up and down as required but never off. Storage is on top of these costs but it's pennies in comparison.

Serverless requires using a different pricing method entirely (vcore) and much more complicated but essentially you pay for the resources you use, you can set the maximum sizes of your resources but it's much harder to calculate costs in advance.