Cellular Plan for Apple Watch

Hi, I have a new Apple Watch with GPS + Cellular on its way soon which I was able to get for free.

Most of the time I'll be able to use it at home (with WIFI) or away from home with my mobile in my bag.

But hoping to use it standalone for running/exercise without my phone.

I'm on Vodafone prepaid and its been fine, pay $250/year and use low data.

As I understand, the only way to use Apple Watch away from home where there's no bluetooth or wifi available is via a link to mobile plan with Voda/Tels/Optus And the plan cannot be prepaid. Is that correct?

Cheapest plans (all 50GB data) I see are:

Vodafone $44/mth + $5/mth Numbersync (to link to watch)

Telstra - $65/mth + $5/mth Telstra One Number (to link to watch)

Optus - can only do Number Share (to link to watch) when you go on a watch plan (have to buy the watch through Optus)

I can see there's another option - you have to set the Watch to Kids mode and can use BetterRoaming for about $11/mth and can use this in conjunction with any existing mobile service you have. I haven't looked into the limitations of this yet.

Just wondering what people have done - are monthly plans with big 3 the only way or am I missing something? Thanks