VertMinMaxSlider

    float sliderMinVariable = 2, sliderMaxVariable = 4, sliderMinLimit = 1, sliderMaxLimit = 5;
    bool DragTop, DragBottom, DragMiddle;


    void OnGUI () {
        VertMinMax( new Rect( 3, 3, 20, 150 ), ref sliderMinVariable, ref sliderMaxVariable, sliderMinLimit, sliderMaxLimit );
        GUI.Label( new Rect( 20, 3, 500, 400 ), "Min: " + sliderMinVariable + "\nMax: " + sliderMaxVariable );
    }


    void VertMinMax ( Rect position, ref float minVariable, ref float maxVariable, float minLimit, float maxLimit ) {
        float totalRange = maxLimit - minLimit;
        float topY = position.y + ( ( minVariable - minLimit ) / totalRange ) * position.height;
        float bottomY = position.y + ( ( maxVariable - minLimit ) / totalRange ) * position.height;

        //the values here of 6 and 12 assume the thumb image is 12 pixels height
        Rect topButton = new Rect( position.x, topY - 6, position.width, 12 );
        Rect bottomButton = new Rect( position.x, bottomY - 6, position.width, 12 );
        Rect middleArea = new Rect( position.x, topY + 6, position.width, bottomY - topY - 12 );

        if ( Event.current.type == EventType.MouseDown ) {
            if ( topButton.Contains( Event.current.mousePosition ) ) {
                DragTop = true;
                Event.current.Use();
            }

            if ( bottomButton.Contains( Event.current.mousePosition ) ) {
                DragBottom = true;
                Event.current.Use();
            }

            if ( middleArea.Contains( Event.current.mousePosition ) ) {
                DragMiddle = true;
                Event.current.Use();
            }
        }

        if ( Event.current.type == EventType.MouseDrag ) {
            if ( DragTop ) {
                minVariable = ( ( Event.current.mousePosition.y - position.y ) / position.height ) * totalRange + minLimit;
                minVariable = Mathf.Clamp( minVariable, minLimit, maxVariable );
                Event.current.Use();
            }

            if ( DragBottom ) {
                maxVariable = ( ( Event.current.mousePosition.y - position.y ) / position.height ) * totalRange + minLimit;
                maxVariable = Mathf.Clamp( maxVariable, minVariable, maxLimit );
                Event.current.Use();
            }

            if ( DragMiddle ) {
                if ( ( minVariable == minLimit && Event.current.delta.y < 0 ) || ( maxVariable == maxLimit && Event.current.delta.y > 0 ) ) return;
                float delta = ( ( Event.current.delta.y / position.height ) * totalRange );
                minVariable = Mathf.Clamp( minVariable + delta, minLimit, maxLimit );
                maxVariable = Mathf.Clamp( maxVariable + delta, minLimit, maxLimit );
                Event.current.Use();
            }
        }
        if ( Event.current.type == EventType.MouseUp ) {
            DragTop = DragBottom = DragMiddle = false;
        }


        //Draw labels using styles from the current skin, change these to custom styles if you want them
        GUI.Label( position, "", "VerticalSlider" );
        GUI.Label( topButton, "", "VerticalSliderThumb" );
        GUI.Label( bottomButton, "", "VerticalSliderThumb" );
        //GUI.Label( middleArea, "", "Box" );
        //Doesnt really draw nicely, when the range between top and bottom gets small, might be better with a custom style
    }