I'd say depends on how good of shape they are in and if they are imports or cbb pair. if they will produce any color morphs will also change the price. also just how well you know the person will change the price. friends will usually sell cheaper to a buddy then they would to somebody they never met before.
but price could range from a couple hundred to more then a thousand just depends on to many variables like if he is just getting rid of them cause something came up where they need quick cash. or if he was planing on breeding them then now they have changed there mind and getting out of it