If you want something that will just simply bolt on, it will matter that it fits your bike.
Otherwise it could possibly require some modifications to fit.
You can usually get the rims and spokes + required hardware to secure the spokes for around half as much as a completed set would cost.
You will have to match up the rim to the hub so they both fit the same amount of spokes and possibly match in how they are arranged.
Then to get them installed and trued on your hubs could be 100-160 bucks perhaps.
Where are you located? If you are in North America there is this,http://www.procycle.us/bikepages/yzf-wrf.html
They offer a 17" wheel set that fits the WR400F for $1099. It uses new OEM hubs Excel rims and Buchanans spokes. Both of which are high quality stuff.
So all you would need after that is tires. And if you want better braking, an upsized front rotor + caliper relocation bracket.
Then there are these,http://www.warp9racing.com/supermoto/supermoto.php
Not as good of quality as the Excel's, I wouldn't recommend these for racing use/jumps personally.
But these ones come with a bigger front rotor, and the neccesary bracket so they are more affordable.
However they list nothing as to what fits what, you will likely have to find these on a resellers site to get the models.