MinMaxSliderAttribute.cs

using UnityEngine;

public class MinMaxSliderAttribute : PropertyAttribute {

    public readonly float max;
    public readonly float min;
    public readonly bool showFLoatFields;

    public MinMaxSliderAttribute(float min, float max, bool showFLoatFields = false) {
        this.min = min;
        this.max = max;
        this.showFLoatFields = showFLoatFields;
    }

}

MinMaxSliderDrawer.cs

using UnityEngine;
using UnityEditor;

[CustomPropertyDrawer (typeof (MinMaxSliderAttribute))]
class MinMaxSliderDrawer : PropertyDrawer {

    private const float FIELD_WIDTH = 32f;
    private const float SPACE_WIDTH = 4f;

    public override void OnGUI(Rect position, SerializedProperty property, GUIContent label) {
        if (property.propertyType == SerializedPropertyType.Vector2) {
            Vector2 range = property.vector2Value;
            float min = range.x;
            float max = range.y;
            var attr = attribute as MinMaxSliderAttribute;
            EditorGUI.BeginChangeCheck();
            position = EditorGUI.PrefixLabel(position, -1, label);
            var sliderPosition = position;
            if (attr.showFLoatFields) {
                sliderPosition.x += FIELD_WIDTH + SPACE_WIDTH;
                sliderPosition.width -= 2f * (FIELD_WIDTH + SPACE_WIDTH);
                var minPosition = position;
                minPosition.width = FIELD_WIDTH;
                min = EditorGUI.FloatField(minPosition, min);
                var maxPosition = minPosition;
                maxPosition.x += position.width - FIELD_WIDTH;
                max = EditorGUI.FloatField(maxPosition, max);
            }
            EditorGUI.MinMaxSlider(sliderPosition, ref min, ref max, attr.min, attr.max);
            if (EditorGUI.EndChangeCheck()) {
                range.x = min;
                range.y = max;
                property.vector2Value = range;
            }
        } else {
            EditorGUI.LabelField(position, label, "Use only with Vector2");
        }
    }
}