Would like a 4 stroke for ~$2000

Just for an idea, I bought a XR250 94 £950. I don't think it is a real loss in power, the 400 might perhaps be too big.

The kdx will run off from the xr. I think you would be taking a step backwards. The xr is more of a play bike vs. the kdx can be turned into a serious woods weapon. If you want to go thumper look at one that is "race ready" as apposed to spending alot of money on a play bike. The xr is in the 260-270lb range and the kdx is 230-240lb range(ride ready).

Good Luck with your decision!

PS>> I know where a very clean,well maintained xr400 is - $2,500 and I've ridden it.

At 215 pounds , you are too heavy for an xr250, and yes it will be taking a step backwards. I had an ' 89 and raced it in 96-98 and it was just out-done by all the newer horses.
You would be a lot better off finding a 97-99 KX or RM 250 for $2k. That would be a realistic price for them. The kx's were the "sh%t " for Hare scrambles during those years......lots of lo-end and handled really well.
I also owned a98rm250 and it is a super nice handling bike in the woods....not a HP king by any means but it has a nice forgiving powerband.
I also rode a 90 model KDX200 in several enduros and HS races and liked the way they handled and the power they have. I like 250's power though.
And weigh about the same as you.

good luck on your choice,

see ya