Do you actually pay to submit to link directories? Why? At what pagerank and what $ value do you draw the line?
Generally, I've found that directories that are worth a paid submission charge too much, but if the price were right I wouldn't pay for anything less than PR5, assuming the inner pages (especially the one my site would appear on) also has decent PR.
How would you link to your site as well? Would you link to your main page or to a (what would you call it?) deep page?
More than PR I would recommend that you guys look at age of directory, the kind of links they have been approving and whether they are spending money in promotions.