The problem is an economic one, one that not many games developers are qualified to solve. Unlike a real person, who has to eat, sleep, and be at a comfortable temperature (or at least not be freezing/burning) to survive, a videogame character can stand around for days at a time, and not do anything without suffering. Furthermore, videogame characters don't have desires. They don't have career goals beyond be the best at whatever the game is (Dragon slaying, Pokémon Master, or even more basic, get out of this Zombie infested hellhole ASAP), they don't have any urge to find love, settle down, raise a family, and so long as they don't willingly do stupid things, they don't have to worry about there health; that they're getting old, or might have a sudden and unexpected heart attack. Videogame characters are effectively immortal.
In the real world, human nature dictates that we always want more. Even if you have unlimited money, you will always find new things to buy. House(s), car(s) etc. you name it, you can have it. Even if you run into a shop, and buy everything you ever wanted, within a month there'll be something else you want. Videogame characters don't have this problem. At best, they already have a house, at worst, they don't even need one. There worlds are usually catered to only sell them useful stuff (sans the occasional novelty joke item, or decorative thing for those who want characters to look good), and there regular expenses only amount to ammo.
In the real world, you get a once a month pay cheque. This pays for food (which gets eaten, and will need to be re-bought), rent or mortgage, taxes and bills. By the end of it you may have enough to pay for things like insurance, fuel costs, pensions and other savings, and hopefully a bit left for spending on whatever you currently want, be it a new game, a few DVD's, or a night on the town. The actually, post expenses profit is minimal, and it takes so long to accrue, that most people won't save it all, as they don't want to live a life on basic noodles in shitty accommodation, as that's not really a desirable way to live.
But back in the game, your character goes into one fight, uses maybe two potions and five bullets, but gets enough money to buy three potions and twelve bullets. From one fight. And considering these are his only expenses every single fight is turning a profit. So while at first you start as a noob, and will have a lot more injuries, and a lot less skill, you will be more wasteful. But as you improve, your expenses go down, but your rewards don't, so your profit is higher.
However, there's no real economy. Nothing new is ever created. So, unlike the real world, where there's always new stuff to buy, in the game, you only have a finite number of items to choose from, and you can actually save up to buy them all. Because the game pays you too much, and yet only charges you for items you use. There are no other expenses, no other things to buy, and nothing else to worry about.
In real life, if you could live forever, and could work forever, it's also possible to have the same effect. But it takes far longer, as the profit margin for each pay cheque is much smaller. Likewise profiting is much harder, because there is never infinite resources. All games have an infinite money inside them, be it respawning enemies, being able to rob the same NPC's every time you re-enter a town, or through winning the same bet over an over against an NPC. The money is infinite, so you can amass the money without thinking. In real life, this doesn't happen. You cannot turn money from nothing, you have to do something for all money. To get a job requires there to be work, for there to be work, there has to be something you can do, that somebody else wants you to. You can't just run around randomly chopping down trees in the forest and waiting for the sky to give you money for it, you would have to actually find someone who wants to buy that wood from you, then get them to buy it, which means setting it at a resaonable price, then paying for upkeep of tools, and paying whoever owns the land. And even after all that, if you found someone willing to constantly buy wood, you would need to find a forest big enough to never run out of trees, or your business stops.
The problem is that real world mechanics aren't fun. Nobody wants to spend forty hours beating hundreds of enemies, to earn $100,000, only to have to lose some in tax and expenses, and then need to spend the rest buying food, rent, and being left with just enough to buy one more potion than you started with forty hours ago. videogames are escapism, and while being able to buy loads of stuff might make them too easy, the reverse would be boring again.
The only real workarounds are imposing tight money limits so you can't stockpile potions but allow you to carry as many as you can find, then restrict them to only findable in certain safe areas, only when you need them. Alternatively, create a fake economy in game, where items become more expensive based on how much money you actually have (in real economics, this is the same reason why we don't just print more paper money and give it out, it devalues a currency, and makes each new dollar printed worth slightly less in terms of what you can buy with it). The third option is to get rid of money altogether, and allow only bartering, whereby if you want an item, you have to give up one, or more, similarly valued items.
If you did scale up the money, I'd suggest doing it in terms of how much you've made, not how much you have. For instance, at the start, a potion costs 100, but then when you've earned 10,000, they go up to 500, and then up to 1,000 once you've earned 50,000, If the scale is slightly warped, each potion would cost you a larger percentage of the money you have on you, so that items actually cost more as the game gets harder, making these helpful items harder and harder to buy up until you beat the game (at which point they can go down, so you can enjoy the post game piss about).
The other option of course is to get rid of all money and trading, and make items available only as treasure found in dungeons, or dropped by enemies, setting a spawn rate on enemies that drop things like potions at such a rate that no (sane) person would want to grind for them.
