Don't forget about boots and gloves. Most track day orgs these days are requiring gauntlet style gloves that extend past the wrist. A good pair of racing style boots (Sidi, Alpinestars, etc) are also well worth the money.
The general rule I've always been told for pants/jackets is that the zipper must cover 75% of the circumference. Different clubs have different rules though. Some still allow textile in the beginner groups while others are requiring 1 piece suits. I'd say you'd be fine just getting a pair of pants and possibly finding a tailer to extend the zipper.
NewEnough sells some really nice stuff and you can sometimes find a really good deal on closeout items.