The Camera Raw tools in Lightroom are precisely the same tools that are in the Camera Raw plug-in. The only difference is the interface in Lightroom. The Camera Raw used in Photoshop is a plug-in, it is not a standalone product that can be purchased separately. It is a companion to Photoshop, and in order to have the current version of Camera Raw it is necessary to have the current version of Photoshop installed.
I currently subscribe to Adobe CC Photoshop but only ever use the ACR tool.
Would it be possible to purchase ACR only?
You're already getting the best deal available.
If you look through the Creative Cloud pricing for the other products, it's:
$50/month for all applications
$30/month for an individual application (like only Photoshop, or only Illustrator, or only Premiere Pro…).
$10/month for the special Photography Plan (Photoshop, Camera Raw, and Lightroom) instead of $30 for just Photoshop.
Because Camera Raw isn't offered (and can't function) independently, $10/month is the best offer they have by a fair margin, even if you don't need Photoshop or Lightroom. If Adobe broke out Camera Raw from the Photography Plan it would probably cost more than it does now, like the $30/month you'd pay if you only wanted After Effects.
If you don't want any kind of subscription, there are definitely many other choices out there for raw developing software.