The cheapest way to get back and forth from the ruins is on the white vans (colectivos) that run down Juárez every 10 minutes from 6am to 6pm. The buses pass La Cañada and hotels along the road to the ruins, and can be flagged down at any point, but they may not stop if they're full. The cost is 10 pesos per person.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.