Is 10 a lot? Depends on the thing.
Kuwaiti Dinars? A decent chunk of change (~$32 USD equivalent)
Iranian Rials? May as well be nothing at all. (~$0.00024 USD equivalent)
One of the issues with declaring that the small number for crew income is unrealistic (besides the prior observation that Star Sector simply isn't a sim) is that we don't have actually any good references to the effective purchasing power of 1 credit for the average Star Sector crewman, or even a civillian. Perhaps you could compare something like the cost of food to a crewman's income, but there's a problem with that: The commercial goods you purchase are all sold in bulk, sold for tens to hundreds of credits per cargo capacity.
And what is one cargo capacity? We don't know that either, other than a few bits of insight, such that some military equipment (large weapons, for instance) are so large that they can take up multiple units of cargo capacity. We don't even know
which capacity it's measuring: Is Cargo Capacity a function of available mass or volume for a ship? It's the same story with Antimatter fuel and capacity, for that matter. Pretty much the only parameter that is spelled out is colony size, measured on a 10^X scale, and I absolutely would not be surprised if that is also axed eventually and replaced by a single abstract number.
So is 10 credits a little or a lot? For the protagonist of the game (effectively a freelance fleet admiral), it's pocket change. For large governments in the Persean sector like the Hegemony it's certainly not even that; they must make a killing on those insane trade tariffs alone! What about for Jane Doe, the Jangala resident? How about John Smith, the Buffalo crewman? Well, we don't really know. We can't really say one way for sure that they're making slave-level wages like you're implying, or if starship crewmanship is a quick path to become a Persean Sector's equivalence to a millionaire, as Gothars jested. Personally, I wouldn't be surprised if standard groceries and such cost merely several milliCredits for people planet-side, with single-family housing ownership costs around the realm of low 100 credits for economy level, and 1000-ish credits and up for luxurious mansions and such.
the fact that he will never be able to get that money because he cant even afford the shietest of ships, speaks a lot.
The initial cost isn't even the biggest hurdle here. A Kite will still cost 2 supplies of maintenance per flight-month, equivalent to 200 credits/month if it were to be constantly flying, which is obviously not sustainable on a 10 credit/month salary.
This doesn't seem unrealistic at all. I'm fairly well off, but I won't realistically be able to purchase, store and maintain a Cessna on top of all the other financial obligations I have now and will acquire in the future, such as various loans and upkeep on automobiles, housing, necessities, hobbies, etc. Kites, obviously, are going to be much more complex, luxurious, and naturally more expensive than that!