phpLD is kind of not so bad compared to other solutions (there is no perfect directory script for me so far). The source code is not very glamorous to read, but is doing the job.
he cool thing is to have many mods, even if many are not free, it's still something.
About session sharing, the price announced is not to expensive for the task, if of course the guy knows what he would need to do (I know the matter, we use a quite modified phpld script here
and we do share sessions with phpBB).