Bring it. Just like any other spare part that you bring, it doesn't count toward your budget. Parts replaced during the race are generally overlooked for budgeting purposes, even if you have to run to the parts store and buy them.
It's the "race car" as it reaches the starting line that is expected to meet budget.
Lemons South 2008 - Fail, Lemons South Spring 2009 - Fail, Lemons Detroit(ish) 2008 - Fail, Lemons South Fall 2009 - Fail, Lamest Day 2009 - Fail, Miami 2010 (Chump) - 2nd!, Sebring 2010 (Chump) - Fail, Cuba 2010 - Crew Chief, Roebling 2011 (Chump) - 8th!, Sebring 2011(Chump) - 19th!