What is the procedure (steps, time and average payment for a lawyer/Accountant to do this) of inheritance taxes (state tax) payment for a foreign investor (non resident exactly from Guatemala, the beneficiary is also from Guatemala) who died owning U.S. Assets and what is excluded from this taxation (U.S. Municipal Bonds, Treasury bonds, etc..)?

Such fees are dictated by the local market. A lawyer/CPA in New York City is more expensive in NYC than in California, which is probably more expensive than in Texas.

Contact a local tax professional (start with enrolled agents, who SPECIALIZE in tax work and thus charge LESS than CPAs normally charge) to find out what he/she will charge, then shop and compare.