It is not possible to access money in a Bancomer Mexican account from the USA.  However, if you have a Bancomer account, you are able to transfer money from a Valley Bank account into that Bancomer account. For an amount up to $1000 dollars forwarded to the Mexican account the charge is $10 dollars. This is cheaper than a wire transfer. The money is available in Mexico in a few hours. Valley Bank expects to open a branch in El Centro in the next 6 months.

By comparison, Union Bank and Bank of America charge $38 for any amount wire-transferred to Bancomer.
Union Bank does not have any special banking relationship with Mexican banks at this time.

Note that Bank of America has branches in Mexico (Mexico City, Guadalajara, Monterrey)  and there is no charge for transferring money from a US account to a MX account with them - it is done by setting up an automatic payment option in their online banking system.
If you want to send money to banks which have a special relationship with Bank of America, the "safe send" option can be used:
The SafeSend service is available free to any Bank of America customer with a personal checking account. It links the bank's U.S. branches to 4,500 locations across Mexico, including branches of Banco Santander, Banorte, Bansefi, L@Red de la Gente, and TELECOMM-TELÉGRAFOS.  When a customer in the United States requests a transfer, the banks in the two countries exchange dollars for pesos. Depending on the time of day a transfer is sent, the money is available in Mexico within two hours or on the next business day. Here is a website link:

Wells Fargo operates a money transfer system to BBV/Bancomer  called an InterCuenta account. (The beneficiary needs a particular type of account with BBVA Bancomer. Such accounts at BBVA Bancomer are El Libreton and Maestras Particulares. Both of these accounts have 10 digits). Here are the essentials:
*       Low flat fee - only $8 to send up to $3,000 per day.
    *       Competitive exchange rate - call 1-800-556-0605, select language, then choose option 3 to get current rates.
    *       No minimum account balance requirements.
        *       No opening deposit required.
    *       No monthly service fees.
        *       The Account Setup Fee is just $10, and there is a low $10 Annual Fee thereafter.
        *       Direct transfer from your InterCuenta Express account to your beneficiary's qualified deposit or debit card account at BBVA Bancomer®, Banorte, or HSBC Mexico.
      *       24-hour service at Wells Fargo ATMs or over the telephone.
      *       Many Wells Fargo locations.
     *       The beneficiary has access to the transferred funds the following banking day.
Note that the InterCuenta account is a sweep account, not a checking account. All money put into it automatically gets sent to the Mexico bank nightly.