You can jump through a small gap in the wall if you're a HU or FI with a partisan or twin daggers respectively. Here's a friend and I figuring out a method for partisan. I'm not the original founder for this! Sorry for the quality, forever poverty net.
No risk reductions, no success rate increases, grinders only, Shop area.
-450k -ish and about 150 grinders or something, probably not much to some people. Got as high as +8 and got hit with a -3 and ended at +3 before quitting.
Music: Etrian Odyssey series.
Also AGDQ 2013, Werster, and Pokemon Gold.