You did do something wrong: the market should always be in order by cost.
When players add new power plants to the power plant
market, players rearrange all power plants in the power plant market in ascending order with the 4 cheapest plants in the actual market.
That's the whole market - all 8 power plants - that you sort. (The lists you provided were possibly sorted within the actual and future market individually, but that doesn't do anything. The point is to make sure that only the cheaper ones become available for purchase.)
While things can get out of order a bit - for example power plant 20 is a 5 and power plant 22 is a 2 - there's no way a 6 is going to come before a 2, and in most cases, it'll be after the 4s too. With the power plants sorted properly, you wouldn't have been able to buy that 6. Your actual market would've more likely just contained 2, 3, 4, 4.
Given that you missed that rule, it's possible you also missed another: during steps 1 and 2, in phase 5, you remove the highest numbered power plant from the market, replacing it with a new one.
Update the power plant market: Place the highest numbered power plant from the future market face down under the draw stack and draw a new one to replace it.
Rearrange the market appropriately (see phase 2: this will change in Step 3, see the steps of the game). Because of this, the highest numbered power plants are collected under the »Step 3« card and become available during step 3 in the game.
This makes it much, much less likely that a 6 even becomes available in the early game. On top of that, it gets you to step 3 faster, when suddenly high-numbered power plants start becoming available more rapidly, making it less likely that one player gets one long before others.