I managed this before reaching the boss at the end of the first mission.
Simply go into the options and give yourself the full five lives and the five continues (so 25 lives, and amazingly your score doesn't reset each time you use a continue), and wade your way through the entire first level (choose the hardest difficulty setting as this spawns more bad dudes - if only Bad Dudes was available on XBLA huh?) before allowing yourself to be killed right at the end of the level. Rinse & repeat, and you'll have that 80k in no time.
Remember, if you're less than 5k short at the end of the level, just finish the level and as long as you haven't used your special attack, you'll get a 5k bonus for that.
Not sure how easy it would be to rack the score up just by playing the game through normally, but I doubt it would be that tough if you remember not to use your specials since that'll give you a 5k bonus each round.