You only get so many of those £0.99 offers before it goes up to £8 without making it clear. I just did a checkout to test and it says "Click here to get your P

You only get so many of those £0.99 offers before it goes up to £8 without making it clear. I just did a checkout to test and it says "Click here to get your Prime eligible items with Premium Delivery for £4.99 no extra charge". Yet clicking that button costs anywhere between £0.99 and £8 without any obvious warning.