A small struct representing a range from min to max.

FloatRange.cs

using UnityEngine;

[System.Serializable]
public struct FloatRange
{
    public float min;
    public float max;
    public float range { get { return Mathf.Abs(max - min); } }

    public FloatRange(float min, float max)
    {
        this.min = min;
        this.max = max;
    }

    public static FloatRange FromTwoNumbers(float a, float b)
    {
        if (a <= b)
        {
            return new FloatRange(a, b);
        }
        else
        {
            return new FloatRange(b, a);
        }
    }

    public float Lerp(float t)
    {
        return Mathf.Lerp(min, max, t);
    }
    
    public float InverseLerp(float t)
    {
        return Mathf.InverseLerp(min, max, t);
    }
    
    public float Clamp(float t)
    {
        return Mathf.Clamp(min, max, t);
    }

    public float GetRandom()
    {
        return Random.Range(min, max);
    }
}

FloatRangeEditor.cs

using UnityEngine;
using UnityEditor;

[CustomPropertyDrawer(typeof(FloatRange))]
public class FloatRangeEditor : PropertyDrawer
{
    public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
    {
        EditorGUI.BeginProperty(position, label, property);
        position = EditorGUI.PrefixLabel(position, GUIUtility.GetControlID(FocusType.Passive), label);

        var indent = EditorGUI.indentLevel;
        EditorGUI.indentLevel = 0;

        var leftPosition = new Rect(position.x, position.y, position.width / 2, position.height);
        var rightPosition = new Rect(position.x + position.width / 2, position.y, position.width / 2, position.height);

        EditorGUI.PropertyField(leftPosition, property.FindPropertyRelative("min"), GUIContent.none);
        EditorGUI.PropertyField(rightPosition, property.FindPropertyRelative("max"), GUIContent.none);

        EditorGUI.indentLevel = indent;

        EditorGUI.EndProperty();
    }
}