Usually you will pay a high price for the Estie 2788 or 9788. I have usually seen these at about $75. I have an LJ with a 9048 extra flexible fine, and it's amount flex is about where I want it--nearly none. If I press down I can strongly underline something, but it's not easy to make these flex. The broader ones might flex more, but Esties aren't known for being extra flexible the way people generally think of flexible.
When I want line variation from an Estie, I use a 2314-B or 9314-B stub (it's oblique) or a 2312 or 9312 italic (medium CI). The 2312 works best, and you might find one at a sane price in the $30-40 range, if you think that's sane. The 9312 doesn't work any better for beaucoup dollars more. I have all four of these nibs. They are OK. The 9048 is a nice fine, near-nail. I have read posts where members wax ecstatic about the flex of the 2788 or 9788. I wonder how much effort it takes to flex them.
I wax ecstatic over the 9460, to me the most perfect of Estie nibs. Dry, narrow for a medium in all five I have, and one so deliciously fine it's almost extra fine and as dry as the Sahara. Different strokes.