I haven't found a quad in my area for under $1000 in years. I'll be about $500 into this project if I bought the 200x front end off the guy local to me. Getting the front end geometry right isn't my strongest area, so I'd rather start with a machine that already has that figured out. I'd love to throw a bigger engine in, but I know next to nothing about them, and some of the interchanges I have in mind won't work for those at all. Not sure if the TRX350D engine is any lighter, but trying to keep weight down even though it's shaft drive which is why I'll probably do a starter and battery delete. I could have always gone with a big bore kit on a 250sx engine but I've had this 350d for a while and my original plans for it has changed. I really love how the 350x engine runs, might just be because it's a bigger engine than the 250es/sx. The 450 foreman engine runs nothing like the 350x though, it runs much closer to the 250es/sx engine. Know pretty much nothing about the 420 and 500 machines but I suspect they run similar to the 450.
I think my area is a bit unique, we have a LOT of auto mechanics, there's so many people that the wadges they make is pretty low for the work involved (rust belt etc). There's a lot of people that work on their own machines at home here too. I find some of the most trashed rigged up machines around here even though it happens everywhere I'm sure.
I've been wanting to atleast try this project for a few years, just looking for a cheap 250sx parts machine hasn't worked out so I went after getting the bare min, frame and such.
This reminds me, here's an interchange I found no one even mentioning online. The trx350/350D shift "cage" does function in a 250es/sx machines. You can see in the pic the opening is wider so the shifter travels further for the shifts. There might be an issue down shifting if the shifter hits the foot peg, but it does fit in the engine in either case.
Also the shift shafts interchange, but shifter sticks out from the engine much further though. I'll probably have to put the 250sx shift shaft into the 350d engine to make it have a good shifter location.
350d left, 250sx right
350d top, 250sx bottom