Well I think that Free is the best for many people, but thats up to the owner of the directory. If it receives a lot of hits daily, and is very organized and there is a big chance that your website will get hit, then I think that in that case a reasonable price should be made.
it should be free unless you want to make dough out of it XD. but well, who don't want to have dough? i'd say make it free first, then when it receives more traffic, start charging. if your directory can ensure a climb in the google ladder, why not?
I think if you are a serious directory owner who is going to sink alot of effort and money into your directory, then why make it free? Sites do benefit from a listing in directories and probably more so from quality directories.
This is completely my opinion but I think that people should make directories that allow people to choose which type of link they would like. There should be the option of either free with a backlink or paid without a backlink but I suppose it would be great if all were completely free too!
I think they should be free and paid... regular links for free and featured ones paid... thats the better way, the people that have $ can afford for a good kind of advertising
A lot of links on directories aren't really for advertising nowadays, they are mainly used to get your pagerank up so to be honest I am not really sure why people would want to buy featured links anyway! People that wish to advertise would usually just send emails/flyers out or something, I hardly ever see many featured links (unless of course you are talking about Dmoz...)!