[DynamicRange] Like [Range], but pulls Min and Max from introspected VarName_min and VarName_max variables. Floats and Ints. Attribute in \Attributes, Drawer in \Editor.

DynamicRangeAttribute.cs

using UnityEngine;
using UnityEditor; 

public class DynamicRangeAttribute : PropertyAttribute  {

  public DynamicRangeAttribute() { }

	public float GetMin(SerializedProperty prop){
		var minProp = prop.serializedObject.FindProperty(prop.name + "_min");

		if(minProp == null){
			Debug.LogWarning(prop.name + "_min not found.");
			return 0.0f;
		}
		return ValueForProperty(minProp); 
	} 

	public float GetMax(SerializedProperty prop){
		var maxProp = prop.serializedObject.FindProperty(prop.name + "_max");

		if(maxProp == null){
			Debug.LogWarning(prop.name + "_max not found.");
			return 0.0f;
		}
		return ValueForProperty(maxProp); 
	}

	private float ValueForProperty(SerializedProperty prop){
		switch(prop.propertyType){
			case SerializedPropertyType.Integer:
				return prop.intValue;
			case SerializedPropertyType.Float:
				return prop.floatValue;
			default:
				return 0.0f;
		}
	}

}

DynamicRangeDrawer.cs

using UnityEngine;
using UnityEditor;

[CustomPropertyDrawer(typeof(DynamicRangeAttribute))]
public class DynamicRangeDrawer : PropertyDrawer  {

  public override void OnGUI (Rect position, SerializedProperty prop, GUIContent label) {
		var reflectedAttribute = attribute as DynamicRangeAttribute;

		if (prop.propertyType == SerializedPropertyType.Float)
			EditorGUI.Slider(position, prop, reflectedAttribute.GetMin(prop), reflectedAttribute.GetMax(prop), label);
		else if(prop.propertyType == SerializedPropertyType.Integer)
			EditorGUI.IntSlider(position, prop, (int)reflectedAttribute.GetMin(prop), (int)reflectedAttribute.GetMax(prop), label);
		else
			EditorGUI.HelpBox(position, "DynamicRangeDrawer can only be used on Floats and Ints.", MessageType.Error); 	
	}

}