Okay I found something worth lookin at for ya. :thumbup:

B&H has at the moment a selection of used Tokina tele lenses for Nikon AF cameras at pretty solid prices. They've got a few examples of the 400 mm f/5.6 for $269 and one 300 mm f/4.0 for $289. I'd go for the 300 mm for the wider aperture paired with an N90s and you've got a solid budget trackside wannabe-pro setup.