Adding a directory to my fitness site?

[baldidiot]

Looking for some advice here - one of my mainstream sites is a UK gym directory and recently I've been getting a bunch of emails from fitness sites asking to get listed. They aren't gyms, so they aren't getting listed but it got me thinking...

Would it be worth adding a general fitness directory to the site?

If so, what is an appropriate "administration charge" () to charge for listings. The site is currently PR4 (for those that care) and more important it acquires backlinks naturally. If done right, what's the right kind of fee for this industry?

Also, bearing in mind it's an established site, should it be added as a subdomain (with a sitewide from the root domain) or a subfolder? Either way I would also build links to the directory - no point doing it if there's no value in the directory, right!

Any PAL homies who offer advice get free listings if I end up doing it