All the features that involve per-use costs of online services require you to have an ongoing subscription. That includes stock footage and text to speech at the moment. Otherwise you could buy Vegas once and cost them money for years to come.

And when I went to try the new text to speech function I was told I have to buy a subscription?!

Yes, that is correct. Vegas Pro's comparison page:

https://www.vegascreativesoftware.com/us/product-comparison/#productMenu

... identifies the features that are exclusive to the subscription model. Recently, a Vegas staff member explained the reason why. Basically, the subscription model involves a 3rd party cost to Vegas Creative Software and that ongoing cost is covered by the subscription price. With the subscription model, you only have access while your subscription is current. If you stop paying the subscription, you no longer have access to Vegas Pro or any of its features like text-to-speech. With a perpetual licence, you have access to that version of Vegas Pro forever without having to pay any more $$$$; but if the perpetual purchase model also came with the subscription features like text-to-speech, Vegas Creative Software would have ongoing 3rd party costs that are unrecoverable from those with a perpetual licence.

From the products pages:

Please see also Product comparison. (Note this comment as well.)

I followed the upgrade offer link and the difference wasn't made as clear as it should be IMO - I appreciate the ongoing cost explanation, however I feel this really needs to be flagged a little more obviously for users like me who've been upgrading for years the same way. I just clicked the same option I always have, but would have spent more time comparing prices if the differences were made more obvious in the marketing blurb I received via email.

Additionally, when I follow the link now www.vegascreativesoftware.com for "more details" - I cannot find the details?

On top of the money I just spent for the upgrade, how much will it cost to avail of the text to speech per month?

Is there a discounted 365 option for users like me who upgraded their Vegas traditionally, but want to access this function?

Try contacting shop@magix.net if you want to cancel the (perpetual) license that you purchased and get a 365 subscription instead.

@pete-g

Right now there's no way to buy features a la carte, so what vkmast says is the answer. The stock footage and music is also quite valuable IMHO.