You get virtually nothing for scrap steel. If you have the room to keep them, the next owner of your car may appreciate getting the original parts. Otherwise you can take them into a recycling center and be lucky if you get $15.
Someone will want the manifolds for porting so that they won't be without a ride for a week. Sell 'em online. Maybe auction them on eBay with a Buy it Now option, or list them here in the classified section.