As you write that your primary use will be landscape work, I'd STRONGLY recommend avoiding a monorail. They are heavy, bulky and slow to set up in the field. Not only that, they are heavy, bulky and slow to set up in the field (get the idea??!?).
I'd also avoid the press cameras (such as the Speed Graphics),as, IMO, they just aren't a good design for field work.
So, that leaves the folding/field cameras. There are plenty of older folders that should be around $500. Occasionally, you'll see newly purchased cameras such as Shen Hao's, for about $600-700. I'd get one of these. (I know that you wrote $400, but you'll probably be buying someone else's problem at this price. And you'll end up buying a "better" one sooner or later once you realise this, fulfilling the old saying that "A fool spends his money twice").
But, don't get too hung up on the camera. It's pretty much just a box. As long as there are no light leaks, most field cameras will do what you want (at this stage).
Way more important are the lenses you buy. Don't get hung up on either the number of lenses you want, nor their age. A 1970s MC lens' results will be almost indistinguishable from a new lens.
If you're a wide angle shooter, look at something like a 90mm. If you're shooting "standard" lenses, look at 150mm (or the real sleepers, the 180mm lenses). A 210mm lens is probably the best "bang for your bucks" lens, as they were a staple back in the film days, meaning that there are both plenty out there, as well as plenty of really good examples. And, they're cheap!
As Konical wrote, do some research. And then a little more. Ask plenty of questions here, regardless of how basic they are. No point spending your $$ twice!!