Who knows without any pictures, a model number, or anything useful. Good to know the same machine made gun barrels, but some information about the bike itself would be more useful.
It all depends on condition, size (fit), model and components. I would not consider $180 to be on the pricey side of vintage bikes. A lot of Miyatas are easily worth $180 or more, and some are not.
I can tell you for sure, a bike that fits someone 4-9 WILL NOT fit someone 5-5.