There are some balance issues regarding the economy in single player... at a certain point in the story it's Arthur just walks arounnd with thousands of dollars on his pocket, without any way to spend them. It kinda undercuts the portrayal of the gang's increasing difficulties but, in more practical terms, it also removes some incentives to engage in the game's many activities.
It would be nice if there was a way to mitigate this problem... Increased prices (ammo could be a little bit more expensive imo, so could some weapons or provisions, as well as Trapper/Fence items), costly camp upgrades, disable Honor-dependent discounts, reduce automatic looting of ammo or the probability of finding valuables on NPC's corpses or saddlebags, etc
I have no idea how hard it would be to implement some or all of these changes. Hopefully someone will do it at one point or another.