Do not do the Showa Exchange Quest, as the pay rates are not worth it at all.

Thieves
(Claw Thieves)-So, you are constantly refilling stars, also buying MP/HP pots, and you have scrolls/equips/etc. to buy. So, seems tough enough. Well here are some small tips that may help you:

Buy Subi throwing stars for training.(will help 'down', the price for refilling stars.)
Despite being weaker, icicles actually cost more to recharge compared to tobis. Try not to use the fanciful stars (wooden tops, snowballs, icicles) as the recharge costs tend to be steeper.
Bowmen
Don't buy arrows from players, since they take more money than they're worth. A arrow can be bought for 1 meso each in the store or made by obtaining 1 prosessed wood (10 tree branches/5 firewood and 1 stiff feather.) Don't use upgraded arrows (Bronze arrows) for training.

Magician
Ice Lightning Mage:
An Ice Lightning mage with their cold beam at level 15 will find fire boars a valuable source of money. At that level, you should be able to kill fire boars in one hit. Ice/Lightning mages should try not to use Lightning Bolt to train at early levels as the MP cost is very high.

Cleric:
Clerics level 43+ with maxed heal should utilize the monkey forest or monkey swamp. Zombie lupins give good drops, exp, and you can mob them up and heal attack them. They drop nice amounts of meso too, and cursed dolls can sell for a nice profit. Zombie lupins are sort of like an upgraded fireboar but for Clerics. In actual fact, Clerics should NOT be losing mesos.

AoE (Area of Effect) When dealing with Area of Effect moves like explosion or thunderbolt, you will save a lot of mesos by sniping mobs instead of jumping into them and attacking. The main advantage of AoEs are their ability to assail monsters, yet giving the mobs no chance of reaching the caster.

Inflation
Like any real world currency, the maple stroy mesos economy is subject to the same flow; because monsters provide an essentially unlimited supply of mesos, the value of the meso has decreased over time. Natural deflation occurs whenever players purchase items from NPCs, or when players who hold mesos no longer participate in the economy, or with an increase in population (not necessarily changing the hands of mesos, but affecting an average income) but mesos are generally created faster than the population can increase to even them out. This leads to continual price rises of various items.

To curb inflation, Nexon provides ample opportunities to begin anew on new servers, yet these new servers ultimately fall victim to the same problems as their predecessors; so, in order to curb inflation on individual servers, Nexon utilizes an escalating tax system in trading, deliveries, and player shops. This has implications for trading; because one can trade in installments to evade taxes, new opportunities for scamming have emerged, as well as disputes regarding the number of mesos one recieves.