Rising diesel fuel costs are draining the Niagara Falls City School District's budget, creating an $8 million deficit heading into the next school year.According to AAA, diesel fuel in the Buffalo Niagara region is now more than $5.90 a gallon. The district operates its bus fleet and has been forced to dip into cash reserves to cover added expenses. Schools Superintendent Mark Laurrie tells me diesel prices have jumped $2 more per gallon, puttin…