USA Transfers are the best and most affordable!! Believe me, been to Mexico a dozen times and they are by far the most dependable and cheapest!!! Trina is the best! You can get all their info just by typing in USA Transfer and getting a quote, confirmation/voucher online!
Listed below are just additional numbers if needed
Entertainment Plus Cancun
914-0290 (local in Cancun)
011-52-998-914-0290 (from US or Canada)