How Much Should I Sell my Conversion Lens For?

I've recently bought a shinny new NIKON lens for my D3100 and since I do a lot of portrait shots, I find I never use my Vitacon conversion lens anymore, so I'd like to sell it, it's a 0.45X conversion lens with macro that you can just unscrew directly from the conversion lens itself, it's multicoated and fits onto a 52mm and comes with it's own pouch.

If you sell it direct to a consumer $8 plus a little p&p if mail order. If to a trader for him to sell on to the consumer, half that if the trader swallows the future taxes on the sale off his half.

I wouldn't pay $4, unless he was buying a high lead item from me at the same time