This quest is the one that bypasses the normal 35, 37, and 39 2nd class change quests. You can still do those quests if you want, each one gives about 50% now so if you want to do 1 or 2 then use this quest to pay to get past a nasty quest (like scholar or duelist) you have that option. In that case just do the 2nd class changes you want to do first, then do this one. 

The quest start in Giran Castle Town in the Blacksmith shop with Blueprint Seller Daeger. He asks you to find his friend Mark. I guess NCsoft ran out of good NPC names. 

Mark is a short run out of the west exit of Giran and appears to be a rather sick dark elf. 

If you talk to him when another player has the mob spawned, he'll say this. You have to wait until they kill the mob to try again. It's kind of like that annoying kamael quest problem all over again. 

Anyway if you are alone or no one is bothering Mark, he gets down to business. 

Then a mob called a Pursuer spawns and starts attacking so you need to kill it. It's green to a level 48. I noticed that if someone interferes (KS's) in the fight you have to redo it. It's not marked as Quest but it gives no exp. 

When the fight finishes properly Mark will tell you to go see Daeger again. He sends you to Grocer Helvetia.

Helvetia is in the Grocery Store, choose "quest" from her options. 

She tells you to wait which is annoying because it's not like you really have to wait, just talk to her AGAIN right away. I chose "hand over the money". If you ask for a credit, she just tells you that you need to pay. I tried this even with a char with all 3 marks and she didn't say anything different. 

Go back to Mark, then back to Daeger. Daeger also makes you "wait". Then talk to him again right away. He sends you to the Black Marketeer of Mammon. Apparently Mark got better super fast and did something nice for you and your 3 mil adena.

The Black Marketeer is just outside the Kamael Guild in town and depending on which race (I was human here) and what 1st class you chose, gives you the choice of what class you want to be, and gives you all three items you need to switch over, assuming you are level 40 already. You will just need to go the head person of your class and switch over. 

If you already did some of the 2nd class change quests, he will refund you money depending on how many you did (1 mark = 1 mil). If you did all 3 like I did here, you get it all back. Too bad it's not the 300 mill you asked for.