There is no The only easy or fast way to get the crown. You have crown would be to buy it from the market which you said is not an option for you. The only other option would be to do the whole questline and beat the final boss and you will be rewarded the crown at the end of the questline depending on your vocation. There are 5 bosses that have to be defeated before gaining access to the main boss. Depending on your levels and vocations you could duo all of these.
As for the final boss it is a team of up to 10 players. I'm unsure what the minimum amount of players would be to do it. The only way to get all the crowns you wanted would be to get a team of players to do this questline and buy the crowns from the other vocations once you've completed it.
Source: https://tibia.fandom.com/wiki/Cults_of_Tibia_Quest/Spoiler#The_Source_of_Corruption