BioShock Infinite: The Complete Edition

This method applies to all the CitC maps but works at the cost of a leaderboard placement. If you want to go on the leaderboards or obtain all 60 blue ribbons legit this isn't a method for you.

If you die without first purchasing a revive you will be given a choice to forfeit your rankings and continue, restart from wave 1, or go back to the hub.
Forfeiting your ranks allows you to continue from the current wave with your weapons, health, salts, and shield restored and any injured enemies recovered 100% (dead enemies don't respawn).
By doing this you can continue infinitely until you complete all 15 waves.

If you want to breeze through the levels I HIGHLY recommend you just mess around the first few waves of Zeal and do any blue ribbons you can just for the money bonus.
Purchase Return to Sender ($1000) and Return for Less ($2000 (I think..) as soon as possible because this vigor alone will help you decimate most things.
My weapon of choice is the hand cannon as it does insane damage when upgraded fully, it holds more bullets than a fully upgraded shotgun, and when combined with Return to Sender you can destroy a Handyman or Patriot in under a minute.

You can get his if you choose forfeit ranking and continue. Enemies will regain all health, but dead foes will stay dead. You'll have infinite lives this way. The hard waves will be ones with Handymen, one on wave 5, and two on wave 15. I recommend lots of running and summoning allies during those waves.