So with the advent of housing and the statement that players can reach 20k a week, I thought I would break it down for a few people.
1) Leves, you gain 6 a day, and can get up to 500 (avg) a leve. = 21k, and thats just battle craft
2) DFR + Needed class bonus: You can make about 10k a day just doing the 4 DFR missions and being a needed class = 70k a week
3) treasure hunt - can make 1-5k a day, but nothing spectacular. If you + 7 friends all get a high tier map and all go killing it. I will just say 7k a week
Now that is direct profit. Subtract out teleports and repairs, and your at about 100k - 3k = 97k.
Now assume you used a full set of i49 jewlery for everything, chances are you now have 7 sets of materia, with about 10% of them being t4 (4/35), and the rest being t3. If you did crafter jewlery, you will probably make more profit than battle craft, but hinder your average group so its a toss up.
All things considered, i see it as very possible to make 100-200k a week just playing casually (6 leves and 4 df dungeons a day with a set of i49 jewlery). I am sure if you wanted to you could easily top 600k a week as a tank grinding df as a needed class for the additional gil bonus.