if i wanna start play this game again, how many bils i need to get a well founded champ?

I think it mostly depends on the character you make. My xenon mule was out damaging most of my 150+ characters without any scrolled or % gear. My160 priest has about 120% int and my damage is crap xD
To answer your question, 1-3 bil for a current character (kaiser, xenon,angelic buster, etc...)
10+ bil for a decent adventurer.

I don't think you need 1 - 3 bil for a current character... You should be ok 1 hitting mobs for grinding without spending anything.

For Bossing, you'll probably want to buy a few 6% stat items for 60~80 mil each (Depends what piece and world) and try scrolling your own crappy weapon through event scrolls.
You won't be the fastest, but you'll be able to do some decent dmg in a party.
If you want to solo bosses, you'll probably wanna spend about 1~2 Bil tops, still highly depends on your character.

If you don't fund a current character at all, you can easily raise your dmg by getting Link Skills considering it takes like... 2~3 days to lvl to 120.
Google about Link skills if you want to find more info.

As for the Decent Adventurer, I agree you need like... 10bil+