Per my info, Colt charged the US govt $25 for each Whitneyville Walker regardless of whether they were eventually issued to Federal Dragoons or to the Texas Rangers. As far as I know the military marked versions were not available for private sale. A few cased civilian Walkers were privately sold. One such Walker is presented in one.of Wilsons.books.Per Whittington, Capt. W. T. Sherman purchased an early "Dragoon" for $28 as a private purchase. As was the practice at the time only enlisted mounted Dragoons were issued govt. revolvers. Officers had to purchase their own.
So in general, I would speculate that $30 would get you a Walker back in the day, or about a months pay, if you could find one.