It's a relative term. We've seen folks on here make incredible museum pieces from the humblest of beginnings, and vice-versa. Do some kits take more work than others? Of course! It's all in how much time, effort, talent the builder wants to expend.
If you're looking to put them on eBay, do a search of each particular kit to see what they're going for. Shipping you can charge a flat rate (and make a couple extra $$) or specify actual cost, then the buyer pays the freight whatever it is.