Between the PS1 and PS2 you have a ton of cheap light gun games to choose from. You don't need anything special either, just a Guncon (or Guncon 2) and the game. Here are a few that fit that cheap/fun criteria:
Point Blank 1, 2, and 3
Lethal Enforcers 1 and 2 (one game)
Area 51
Time Crisis (1, Project Titan) for PS1
Time Crisis 2, 3 FOR ps2
Vampire Night
Ninja Assault
Maximum Force
Dino Stalker