You know, putting aside custom pieces and repaints based costs, I've just realized that I don't think I've paid much over retail for anything in my collection, surprisingly enough, and I've been collecting since the 90's. There have been a couple of times where I have been willing to go higher than original retail by a decent amount, but it still wasn't enough to secure the pieces in question, so I simply let them go. I'll either find them later for a price I'm comfortable with, or not at all. But that's okay, I don't have to own everything I like.
Keep in mind I'm not trying to sound superior, I'm not judging anybody that does pay inflated aftermarket prices, and I'm not fundamentally opposed to doing so, if it is something you truly want and you have the money to treat yourself with then go for it, but I guess I know myself pretty well, and I've just got a good handle on exactly what I'm actually truly interested in owning long term, and on the odd occasion where I do miss, my webfu is strong enough to usually still find one somewhere for retail, or if I can't, I'm patient enough to wait for what I consider to be a fair price, even if it takes months, or in a couple of cases years, until an opportunity pops up, which it almost always does. I'm plenty patient, self aware as far as my tastes and collection goes, don't buy into hype or the old 'keeping up with the jones' mentality, and collect for my own pleasure, not for anybody elses, so I think that has helped keep me grounded and realistic as far as what I buy and what i'll pay.
But that's just me. Everyone has their own journey, their own priorities and situations, so as long as it works for you and keeps you happy that's all that matters, really. To each their own, as they say.