Rules (+ Dashboards)
You could continue using ActionTiles and just use the Rule Engine side of SharpTools. Based on example WebCoRE piston, it looks like this rule wouldn’t use any premium features of the rule engine like variables or HTTP Actions, so it would likely even fall in the free tier.
That being said, I would encourage you to take advantage of all the features of SharpTools. If you use any of the more advanced features of WebCoRE like variables or HTTP triggers/actions, you’ll likely want to bump up to the premium tier of SharpTools at some point.
And there’s some really neat features in the SharpTools dashboards you could take advantage of as well. The best feature might be that SharpTools is already migrated to the next-gen SmartThings connection, so it will continue to work after the Groovy shutdown unlike some other apps. 
Fully Kiosk DTH → Driver
Based on the piston, I also suspect that you’re using the Fully Kiosk Controller DTH, right? If so, it will also stop working when Groovy shuts down. That being said, some people have switched over to the Web Requestor driver which can make HTTP requests on your LAN to the Fully Kiosk API.
If I remember correctly, a playSound URL would look like:
http://your.ip:2323/?cmd=playSound&url=[url]&password=[pass]