Best character to spend a $100 on?

100 bucks isn't getting you anywhere.

Go make a veno and grind money for a herc, then you're good.

guessing Teny meant do a veno and dont use the money, save to hercules/phoenix in coin (you can buy gold with coin).

I dont think this game is worth spending money on it... those 100 bucks could last almost a year in a p2p game, this game is to waste 50 bucks a month, considering events, the need for charm (one charm can last 3 hours top in a zen party) and refining. Theres actually no "fast" way to get higher lvl.
If you consider the benefit of selling gold its about 130k each gold, which means HH mats cost 300-500k depending...
Maybe Herc would be worth getting, but yet it wont be a skyrocket fly to high lvl, venos after 70-80 are slow levellers.

If you really want to make the money stretch, then avoid anything that can be interpreted as a vanity item. Never buy clothes, flyers, mounts, or misc stuff that doesn't directly affect character play.

Getting the character build guides and carefully studying the implications of different build types will prevent you from ever needing reset stones. Don't invest stat points unless you understand exactly how your char build works.

Having one craft is valuable, more is a liability, either way buying a super inventory stone really helps you carry mats and drops. With that, you can avoid the super safe stone and just get the first two in game safe expansions by trading DQ drops.

Never do Dragon Quests, most of your cash flow will come from selling DQ drops in your catshop for 150 to 200% of face value, maybe even more. Pay attention to mobs that drop DQ items often and farm them until you are +5 levels, at+6, move on to other mobs. At +3 to +5 you are losing 10% of all normal drops, and it gets worse as your level rises.

Most char's, fighters especially, spend a lot on equipment repair, veno's don't. My veno has a net positive flow of potions, and sells them regularly. Veno's need a lot of cash for pet skills, but generate cash better than anyone else. They are also pretty fun to play and pet control is an elegant skill.

If you are going to have a variety of pets you will have to break down and get the super cage. This isn't required, but it really helps. The tradeoff is you can't keep a bunch of pets trained to your level if you are doing quests, and you can't level quickly if you are avoiding quests while you train pets. Your general limit is 1 flyer, 1 water, and 2 land pets. Any others will be much lower level, which isn't always a bad thing, especially if you want to use them to capture rare pets.

Fast transportation doesn't really become a big issue until you start World Quest at level 70. It's nice to have before then, but with patience you can live without it. You could still avoid this by having an elf with maxed flying speed as an acceptable tradeoff.

If you have 3 or more kill quests in the same area, it is worth buying a Training Esoterica and doing them all while it lasts. If you have time left over, keep grinding for the best DQ drops. Remember your catshop is your profit friend. Sell nearly everything you aren't going to keep there unless it is real junk.

While dying regularly or often allows you a chance to earn extra Spirit, not dying lets you gain levels faster, and I find that my veno died least often of all my char's.

I'm out of time and I hope these suggestions help. I can't argue with the earlier poster who said a mount pays for itself eventually, but I don't agree with him either. If the stuff you are gathering has good value and you can get enough, he may be right.