so I have a project, it works all the way to field tests. I have a schematic that shows how I have the Arduino and the wiring setup with the components. I need to make it all a lot smaller, fit in a case of some type and be a lot cheaper than buying an Arduino for each unit.
So you need to design, or have designed, a new board (and possibly packaging) that omits all the Arduino components that you don't need, includes all the additional components you DO need, provides some mechanism for loading the firmware socket for chip, ISP connector, etc), meets your desires for size, and is "manufacturable" by one or more definitions (that will depend on target price, target number of units, etc.) Then you need to find a way to get the actual manufacturing to occur.
You can learn some or all of those things and do them yourself, or you can hire consultants and/or design companies to do it for you (at significant costs/etc.) These are significantly difficult tasks; it's pretty much a myth that a sufficiently clever design is profitable without all this non-design stuff happening as well.
A start would be to look at how the "dangerous prototype" folks have their stuff built by Seeedstudios.