I try to support the vendors first, except for parts that could have 30+ year-old plastic or rubber.
If I get sticker shock from the price of a part, I lean toward a crossover as long as it's not more expensive in the long run (as Josh mentioned.) I also prefer crossover parts that have a lifetime warranty that can be sourced from Autozone or Advance (like the Eagle starter)... worthwhile wisdom I learned from Bill.