First off, I'll start things off by saying that you cannot make a guide on selling PGC. Everyone has their own rates, and especially the buyer's rates, for that matter. Seeing your prices, my only guess would be that you're a former void player. I've been observing prices since the beginning of this server, and also as a former consistent PGC seller, I can say that these rates are completely inaccurate and do not fit this game whatsoever.
Before you start including math into your equation, you forgot to take into account that this is an entirely different game. Formulas cannot be applied to each and every game in existence. The current way of making credits does not, and never has, supported rates this high. Even the current rates you're listing 9(i.e 3b-4b for $100) shouldn't be that outrageous, but PGC sellers became more rare over time. This timing was not good, as it lined up with void's closure. Not to mention, we just had a big credit sink event, so no one even has the credits to make up for prices this high.
I've seen void's pricing on things, and I will tell you right now that bringing those prices over to this server would most definitely would be the death of the market as a whole. If you think PGC sellers were scarce before, you would be completely wiped out. Not a single person would buy off of you for that, and if anyone ever did, they would be extremely desperate. Taking advantage of that would only reward you with bad reputation.
I saw no mention whatsoever about how the current way of grinding credits could support these rates. If you're going to make a post like this, you need to have information to back it up, because you're only misleading people this way. A post like this can mislead new sellers to think that it's actually okay to sell for these prices, but it will only make people grow cold towards them.
I agree with Virly and Tsugu on the points they gave. You should not be trying to get more profit out of something than what it's actually worth, because it just breeds more and more greed. I understand you want to get as much as possible out of the money you're throwing into the game, but you have to take the f2p players into account as well. They do not have a means to justify such high prices, so they also try to get the most out of their credits. It may not be the same to you since they got it for free, but it takes a lot of grinding just to get 2b alone(which was the old rate for $100). It actually saddens me to see things have gotten this bad when I can't sell any myself. If I could help it, I'd be consistently selling codes at the old rate.
For anyone who still cares about the f2p players wallets, here's the old rates:
$5 codes -- 90m~100m
$10 codes -- 150m~200m
$20 codes -- 300m~400m
$30 codes -- 475m~600m
$50 codes -- 900m~1b
$75 codes -- 1.3b~1.5b
$100 codes -- 1.8b~2b
sorry if these are not completely accurate, this is off the top of my head from when I used to sell codes