Honestly, I don't think it's for "rich" people. Take me, for instance. Just yesterday, I had 20k MP on me. Only 20k! (cause I spent everything else on map instructions) However, I used that to restock from fairly easy stores, such as soft drinks, halloween treats, traps, etc. This takes a whole bunch of patience, if you didn't know. Then, with around 5k mp left, I went and did some GOOD dailes, which earned me around 30k more. I did a whole bunch of secret santa quests, till it asked me for multiple 10K+ items; and my MP total went up to 200k. On to leprechaun quests, and earned around 75k RP. Sold that, and earned 600k MP.
I did this over and over after my quests "ran out of time" for me to start again, and I eventually ended up with 2 million from that run, just from questing and restocking and questing again. Now, today, I have around 5 million. And I didn't even have to pay a single cent~!
And as for the items that are fairly expensive, that's been pretty normal. Not every quest will be easy and ask for cheap items. Or else everyone would resort to questing as their profit. You don't even know how many times I've spent 15K mp on a quest, and received around 2k mp in return. But it opens up a new chance for a new quest, which hopefully will be better than the last. And usually, in the end, the good earnings balance out the bad ones.
Lastly, the only real time an item would go insanely high priced is when it's featured as the item of the week, or an item for the Greedy Fairy~!