the two long guns are commonly known as fowlers and on the local market would be in the $200 to $300 range. The two handguns are of a pattern common before 1800 but they also don't appear to be in very good condition and one appears to be missing its hammer (or #### in flintlock terms). Their value would hinge considerably on their country of origin and / or use. If of middle eastern origin, then probably in the $2 - $300 range. I have 2 Turkish pistols of similar appearance, that I bought in gunshows for $150 and $300 respectively. If the pistols are associated with northern Europe, I would put their price several hundred dollars higher. To know that you need to look for maker's names and proof marks
Almost forgot; the powder horn if old, would probably run around $100
cheers mooncoon