Balancing this isn't easy, because some of the fundamentals are broken - the mining economy in particular, but to my mind that is just a symptom, not a cause, because they just have high prices. The problem is that the profit margins are ungodly.
The galactic average for Polymers is 308 credits. The profit margin on these, if sold to any of the top 25 prices as listed on EDDB is 2,793%, and 24 of 25 of those stations have demand that is higher than 250,000. Per ton the profit isn't that high - it's only 8,600 (ish) credits over galactic average, but compare it to gold (unmined). The highest profit you can make on gold is 4,250 (ish) credits, and you need to buy it at the cheapest place possible and sell at the highest place possible. And you need to make the money to even buy one ton of gold to start with.
We start the game with 1,000 credits. That buys you 3 tons of polymers at galactic average prices. Sell with a profit of 8,600 and you're one sale away from having 26,000 credits. D-rate everything, c-rate the FSD, sell your lasers (costs 21k, so you have 5k profit left) and fill the ship with cargo racks and do one more run. You're now carrying 12 tons and will make a profit of 103,000 credits.
Who wants to haul gold when you can haul plastic? Who's going to rob you of your precious plastics? No self respecting pirate will look at a haul of plastics and think "I'm having that!"
Buy a D-rated Hauler with a C-rated FSD for a one time run for a 176k run and upgrade to a mining Adder. Fill that with 8 tons of painite and get a nice 4 million credit for your troubles. Spend about 1.5M on a mining Type-6 with 64 tons of cargo space. Fill that up with mined painite for 32 million profit. Spend 30 million on a Type-7 painite miner that carries 224 tons for 112 million credits in profit. Spend 104 million on a Type-9 miner that can carry 640 tons and can net you 320+ million of profit with painite.
This can be done in less than 10 stops, not counting refuelling and finding a station to buy the ship and the right equipment.
We've gone from a Sidewinder to a Type-9, and barely spent any time in the Sidewinder, Hauler, Adder, Type-6 and Type-7 other than to fill the cargo hold once, a bit of mining and a bit of travel.
Now what? Where do you go from there? Anaconda and Beluga? They're more expensive, but since making money has essentially become the only focus of the game, why pay more money to make less money? The Corvette is more expensive but can't carry as much and thus makes less money. The Cutter gets close, but without dropping the shields, it's still hauling less stuff when mining. And those two need rank, which is just boring work anyway.
The only "upgrade" from this 6 stop progression is a fleet carrier. If you want to do something else, you now have the funds to do pretty much anything you want. The only thing you can't realistically do is PvP, because you haven't unlocked the engineers, but that's it. You have the funds to go toe to toe with anything else the game can throw at you, and you don't ever have to worry about funds.
It snowballs completely out of control and leaves those who haven't figured out how to do this so far behind that they think the game is rigged against them, while those who know will jump so far ahead that they never learn to appreciate any of the small ships.
To me, this is the root cause of the game's main problem. Progression has one of two paths - one that is slow and (to some boring) and one that jumps you to the end game almost immediately only to reveal the lack of an actual endgame.
Is this the game you want to promote? Is this the game you want us to buy? Is this the game you want to play?
To my mind, if this is the intention, then why not just start us all off with two billion credits and be done with it, because if the credit inflation isn't fixed, you might as well.