According to this United States Army history, the exact numbers will probably never be known, however, over 50,000 slaves were sold into the U.S. armed forces by their masters during the Civil War.

https://books.google.com/books?id=C1IJAQAAMAAJ&pg=PA28&dq=claims+%22slave+owners%22+enlistment&hl=en&sa=X&ei=EZLOVL3OKYyiNqGygYgB&ved=0CFEQ6AEwBg#v=onepage&q=claims%20%22slave%20owners%22%20enlistment&f=false

That's any where from $5,000,000 to $15,000,000 if you use the $100-$300 bounty normally used.