1. 90's X-Men vs a Sentinel and not for $5k+.
2. 90's X-Men vs Cameron Hodge (X-tinction Agenda, w/ spider body).
3. Spawn blowing a hole through Violator, who holds Simmons' heart in his hand.
This is easy and very love of the characters driven:
X-Men vs Dark Phoenix (original comic accurate line-up/designs only)
Storm vs Calisto
Superman vs Batman
Harley, Ivy, and Catwoman vs whomever they want
She-Ra vs Catra
Power Girl versus Supergirl or Wonder Woman or Big Barda (PG vs Someone)
Donna Troy versus Wonder Girl (Legacy)
Jessica Cruz versus Arisia Rrab (Green Lanterns)
Raven versus Starfire (Titans)
Black Canary versus Batgirl or Huntress (Birds of Prey)