something less than $4 mil if a guy indicates he will sign for slot, if a guy indicates that he may not sign, it may take upwards of just under $12 mil to sign that kind of draft pick.
Now if you should sign your #3 pick, that depends on the quality of the draft class. In some class the #3 pick will end up being mearly OK, in other classes, the #3 pick may be a hall of famer.