I need this too, there is a topic here where you can find the idea.
The idea would be to create two fields and add them to the search type (form). Set the same data storage as the price field (or the field that should be on a range-search). In fields view, press 3 (Match + Stage) and set match to highter / lower.
I tried this, but unfortunately it was not working for me - maybe i should play around again and see if i can make it work.