I dont know i have WLs and Sorcs pretty much, and i think that the game is playable even with not that expensive gears, the rest you get it pretty much selling and reselling or investing. The problem tho is that you need to be pretty much 24/7 to get zeny cause...reasons. I have a friend that pretty much the only thing he do is MVP and he got like 4-5 mvps, farm gold scarabas and stuff. He is online all day pretty much lol. I have other friend that only hunt MVPS and have a bunch too, other that pretty much invest all weeks on the machine and buy like a bazillion of tickets (wich i will never do and thats why im frickin poor xD) but as the game is made, it take a lot of effort to make zeny. Of course there is the ones who take the easy way and just WPEed his way to the top, i mean both ways are available so, if you are such in a hurry go for it.
I can do OGH with my sorc with a +7 thanatos OH staff and a pair of +6 runaway magic int boots (that i make on my first runs to ogh with my friends, i was lucky i guess), i do ghost palace and GT with my WL for easy money too, if you have more characters to farm those low level instances you can pretty much get zeny fast. +9 FAW and Elviras are expensive tho, but you can get a couple of mills on a month to maybe buy it if you do instances regularly. I also invest once a month (lol) a good amount of zeny and is pretty much doubled (never do thaaaat much zeny because you will never change tickets lmao)
Certainly there are some classes that have it difficult, but GX is not one of them, i mean i even try OGH with my WL (i can do it with a trio of Maestro/AB) but solo i just made it to the Bloody knight floor, i manage to kill one of the mini boss there but having problems to find the second one, im pretty confident that if i manage to make it to amdarais i can kill him (because i do it previously with my pals) but i lack of the DPS when i dont have a stringer to kill the shadow monsters, before. Anyway, the thing is that characters depend on gear, agree, but having low-mid budget gear doesnt mean you CANT do instances, hazy forest is retardely easy on a GX is pretty much cloaking exceed till the miniboss and then ctrl-click till is dead with that holy katar, i used to do that on a 130 GX so, the coins and the OCA chance pay the EDPs there.
The other thing is, why people always forget this is a game you play with friends (that you bring with or you make) all this "i want the 5b gear to solo all the game" is, i dont know, weird i guess. I mean if you can go for it, if you manage to get a huge fortune (WPE or just farming) yeah do it, if you have fun, i mean i found it more like a challenge on some chars like Fuyukuyin does, but i found that friends is better than gears in most cases XD. Imagine that you can do malandgo and sell each seagod in like 3m, so in 2 rounds you get 10, and you can fam that once a week with i dont know 10 characters and make some money (but that instance need more people unless you are really well geared). I dont know play with others untill you get your huge fortune.