Yeah, never once found a reason to buy a legendary weapon. Based on the price of them, it sounds like they really want you to craft them anyway. At the end of my last 100 hour playthrough I was using all crafted Legendary Iconic weapons. In fact I wasn't sure of the point of legendaries other than the iconics in general.For what it's worth, it doesn't seem like money is all that important outside of buying cars...which at least IMO are basically worthless. There are some really high end weapons that cost a few hundred grand, but they're aren't much (if any) better than weapons you can find out in the world. You can potentially craft better, too.
Money, gear, and "builds" are a lot more important early in the game. The southwestern part of the map is littered with missions that require a deft approach until you hit level 13-14 or so. Plus, the gear you get from them you can't even use and the XP is the same. It's pointless to even bother. Later in the game you'll be able to kill every single enemy in those areas with 1 hit. You have to intentionally choose bad perks not to be overpowered.