how do i get my money back , when i was arrested, for possession of a controlled substance

I am not admitted in the state of Nevada, but in the State of Connecticut, where I practice, here is how this works.  Your property may have been seized either as evidence, or subject to an asset forfeiture proceeding, or both.  If it was seized as evidence, the seized property form in the court's file in the clerk's office at the court should indicate how it was disposed of (returned to the state, destroyed, returned to the defendant) at the time that your plea was entered and accepted.  Thus, the time to deal with this issue was at the time of your plea, and it may be too late to do anything now.  However, you should be able to access a copy of your file either in the clerk's office at the court where you entered your plea or at the facility where the files are transfered after they are disposed of.  In any event, your first step should be to contact the clerk's office to see how you can obtain a copy of your file and therefore the seized property form which will indicate how the property was disposed of.

On the other hand, your money may have been the subject of an asset forfeiture proceeding, which is a civil action which allows states to seize the proceeds of illegal transactions (such as drug deals).  However, if your property was the subject of an asset forfeiture proceeding you should have been served notice of such.

In any event, you should contact an attorney to help you determine the basis for which your money was not returned by the state and if there are any methods of recovery available to you at this time.

I am not admitted in Nevada.  But what appears to have happened is that the police took the money as "fruits" of the crime.  In many states the DA's offices are permitted to keep the money.  You need to contact the lawyer who helped you plead down the offense and see what the state and local laws indicate with regard to the seizure.  Recovery of the money may be difficult at best.