If I buy an annual prepaid product that includes a high overall price plus tax, will it mean that I will be billed annually with my card?

You should be able to buy just one year's worth, and the quoted prices should state clearly if it includes tax or if that is added.

It should also be clear how you renew the subscription or end it, as you choose.

If the sales literature is not clear on these, don't touch it. Decide if it is something you really need or merely want, espcially as you say it is expensive; and if necessary, find another supplier or simply do without.

Most likely