my opinion $10-15K, but I'm cheap.
And as far as flipping goes, I doubt I'll ever have the spare coin to strait up purchase my dream Motion or Yenko, with kids, morgages, life, and whatnot. But I'm a quarter of the way to flipping my way into one. And flipping is a pretty fun means to an end.
now I'll go back into a dark corner and continue lurking.