That is the first key cache I have ever heard of,that is pretty neat.Not sure how to date old skeleton keys but someone should be able to help you out. I don't think they are silver,unless the can they where in caused them to rust like that?.Cool find
I would say metal (Iron) anywhere from the 1830's to 1930's Big range I know.
The first two are door locks Standard mortise house lock Front door back door, the third seems to be a cabinet key with the forward slot. (the least intricate/ simple to pick)
Not a lot of value at all. What I know most about keys is that the more intricate/ complicated the unlocking mechanism is, the more it is worth.
Back in the 50"s you could buy skeleton keys at Woolworth or Ben Franklin dime stores. Of course I had to have them. Pack of 2 and would open most mortise locks. Made of steel, I think the cost was .25 cents. As a kid the idea of opening a locked door was very interesting. Having a detective mentality I needed all the tricks I could find. With my friend Susan we made a foot print cast of a peeping Tom with plaster of Paris and gave it to the police chief so he could capture him. I'm sure it would have helped but the suspect drowned in the lake fishing. We were probably right as the case of the peeping Tom ended.
I had a lot of fun being a kid.
The teeth on the two longer keys look identical, just the shafts are different lengths.
Cool find! Maybe the person buried other things around there, have a look around with your detector.