I don't think there's a charge for "wanted" items...but you have to register separately as the forum registration simply won't work for the classifieds. I tried for years to make it a single registration and was successful for about a week. The forum software had a critical update which broke the single registration and the writing was on the wall....dual registration.
If there's a charge for a wanted ad, just go ahead and place it. Notify me by email and I'll return your payment or approve the ad...whichever is necessary.