Have seen a few people mention this, but TikTok and Instagram are great free marketing tools. Instagram now has a 'Trial Reels' feature where if you use the correct hashtags, your content can be pushed out to a totally new audience. I would recommend talking about it yourself with maybe a green screen of the plugin rather than just a video of the plugin itself as that's always more engaging.

As for selling, I haven't seen anyone mention MuseHub, but they pretty much do all of the legwork like pricing and all you have to do is essentially upload your products.

Selling your VSTs on platforms like that and others also provides various marketing opportunities they may have internally.

Best of luck!