Do you have “badass crater of badassiitude” DLC?
If yes, go back to normal gameplay mode. go to the beatdown, then pyro petes bar. There do the bar brawl mission thing until it is level 50. The level 50 mission can be played again and again and again. If you are doing well, you get those 613 coins in less than 2 houres. (maybe a little more due to your level).
Then RETURN TO UVHM and visit the torque vending machine. if it has a unkempt herold, buy it. if not. save, reload. look again at machine. soon you will have an unkempt harold of your level, will help a lot getting enemys down. If you did not reach pyro petes bar right now in UVHM, then there is another vending machine available right from beginning, just take the car and look for it.
If you are singleplayer, you may encounter enemys who can not be taken down with one life and who have respawned to full power when you return. if you are stuck due to such issues, then do the following:
-> Create second character (on xbox you need a second account too which does not need to be registered online, just call it coop).
-> If enemy respawns, call in second character and place him near to the enemy at a safe spot. Often it is possible to do so without entering enemys aera. If this character is near enough, the enemy may not respawn anymore
-> Now just forger about money and dying and costs. Run up to that enemy, pump him full of lead until you die, return and continue until finally you get him down.