This and much more should be possible soon once the shortcode field has been implemented (Render template shortcodes in form - #2 by Daniele) It’s a long thread, basically it will allow us to render any kinda template inside the form. In such a template for example, we could create a custom range filter, render it in the form and pass the value into the form as well.
Rangefilter would still be nice as a standalone field though so let’s see which way Daniele goes. If shortcodes are implemented first, I’d be happy to help you set up the range field.