Fannie Mae foreclosure advice needed!

I’m about to make an offer on a Fannie Mae foreclosure. However, I understand Fannie Mae doesn’t budge much on their asking price, and I need to really lowball on the bid in order for this to be a profitable investment. Has anyone dealt with Fannie Mae properties? I think I have a chance since my offer is cash, and banks will not fund this property since it needs a new heating system and possible septic. Thanks!