I usually figure about 1/2 of the new cost, but it depends upon the equipment. Stuff that wears out might have a lot less value than that, some that doesn't, more. I'd say on the BRS site things tend to go for less than they might on places like RC, but then again you have to deal with shipping and people you might not know. I check for the new price with the usual on-line sites. Some equipment that has become superseeded by better stuff might be worth very little.