If you hit a rock or some other obstacle with the shift lever, it is less likely to bend or snap off, and leave you "shiftless"... ;-)... What is the advantage of a folding shift lever?
Here's the shift lever thread from the old forum:
Ater a quick search on eBay, it appears the YZ 250 shifters are about half the price of the IMS shifter.
This is the one I bought (about 4 years ago)
It's for a TTR 125.
The IMS part # is 317314.
I purchased it here (about half way down the page):
http://www.motorsports-network.com/cgi-bin/dbsearch.exe?mdb=/ims.mdb,tbl=IMS,dbtype=2000,template=/aIMS/returnims.htm,DB_Product=Flightline Shift Lever
It was about $30. There may be other, less expensive choices.