It is indeed quite expensive, but beside Node-RED dashboard (like @Brian Pribe wrote) we don't know about any other open source / free alternatives to it. I know that there are a lot of smaller vendors out there as @DanielH is showing me regular.
the issue seems to be also a little bit more difficult than one might think:
1. it needs to be a frontend, that can be modified by someone from an engineering background (not from IT). even though we use svelte / sveltekit ourselves for our Management Console, we don't think that any non-programmer can use it
2. there is also the topic of the backend, with multi-user, SSO, etc.
If you know of a solution (or build one) that allows easy creation of a dashboard with a couple of buttons (e.g., for stop reasons) and allows sending messages (and receiving) from the UNS / MQTT, you have solved a pretty big problem for a lot of people in the industry. Node-RED dashboard is nice, but is still too complicated and really easily falls apart on medium complexity cases (e.g., a popup should open to enter stop reason for a machine, scaling out a dashboard across 10s or 100s of machines ,etc.)