Well, the topic is totally blown now, but I noticed that Texas Lawdog was looking for Trapdoor, Krag and Enfiled bayonets. These things are all over the place, they are not scarce, ebay always has them listed (buyer beware). Right now there are several Krags for less than $100. If you don't mind, there are really great quality repro's, correctly marked for the reenactor. Enfield's are easy to find.
For a Krag repro I suggest you visit:
www.ima-usa.com/product_info.php/cPath/4_100/products_id/2182 for about $80, for a Krag real deal I suggest:
www.gundersonmilitaria.com/bayonet.html at about $140.
Be careful about Enfield bayonets, the WW1 sheaths were all leather I think. Plenty of Enfield bayonets were refinished and given a new sheath for shotgun use in WW2.
Bayonets for the AR-15 are pretty reasonable, although quite a few are selling modern bayonets (I don't know if they are military spec) as military, but they are not that expensive.
As a buffalo hunter I always carry a bayonet for my AR-15 just in case the Comanches are thick and I am running low on ammo.