This challenge was tough. I'd say it was almost as tough as beating the Devil on Expert in Cuphead. Probably took me 30 hours plus of practice to get this. It IS, however, possible!
The trick is balancing health and ammo and learning the patterns of what zombies come where. Especially the Gas Tank (exploder) Zombies, you need to know where they come and how best to use them.
Some basic tips:-
#1 Try to hold off using your first GBR (Shield Heal) for as long as possible. You really need that shield at the end when things get mad.
#2 Yes, you can do it in less bullets, but make your life easy. Max out the handgun bullets to save the heavy stuff for when you're under pressure.
#3 Towards the end, try to keep Sparkshots for single zombies and the Flamethrower for groups.
#4 Try to hold off using the rockets - they are great for getting you out of a pickle, but kind of a waste if you use them when you're next to a Gas Tank Zombie, which would have done a similar job but only cost a splash of flamer fuel.
#5 Spark shot is great for Pale Heads and armoured zombies.
#6 Try to use Gas Tanks to take out Pale Heads and Armoured Zombies.
#7 Use the Uzi to either carefully pop headshots when you're not under pressure or to 'spray and pray' at a Gas Tank when you're swarmed.
#8 If you DO need to fire a rocket, aim at the ceiling or floor - this seems to give a bigblast area and you might kill some zombies you haven't even seen.
#9 If you ARE short on ammo or weapons, but Shielded and on full health, you can let a Back Pack or Gas Tank Zombie grab you. This makes them drop their load without costing you a single bullet.
#10 Practice corralling zombies into an area with a Gas Tank. This is probably the key skill you need to succeed in this challenge.
Watch the video a couple of times, play it yourself, try to learn the patterns. If something different works better for you - do that instead. Good luck and let me know how you get on in the comments.
Detailed Tips for each wave:-
#1-10 Use the handgun, try to place your shots. Try to get the Gas Tank guy to drop his can between the counter and front door.
#11-20 Start by using the can dropped already to take out some armoured guys. See video for how to do this. Avoid using your first GBR mix if you can. Use the spark shot dropped by the backpack guy in this wave to take out any stragglers.
#20-29 Check your Gunslinger shots in the records. If you're where you should be - around 45 shots. Use the handgun to kill the first three poison zombies that come in from the backdoor. If have enough shots, kill another couple with the handgun. Otherwise, move to the Sparkshot and get the backpack guy's Uzi. Save the shotgun shells for later and focus on the Sparkshot and Uzi. Save half a clip of Uzi ammo if you can.
#30-39 Start by killing the backpack guy with the Red Herb at the backdoor with a Spark shot or shotgun shell. Then run to the counter and try to herd the zombies around it. Use the exploding Gas Tank guy to take out as many as possible. If you take out the right zombies another exploder, and a Pale Head will appear. Herd the remaining together and use the 2nd exploder to take them all out.
#40-49 Begin by taking out the cop coming through the front door with the flamethrower in a backpack. Use the Uzi if you have enough shots. If not fall back on the Shotgun. If you're really low on ammo, but have a shield and health let him grab you to drop the pack. Grab his flamethrower then run to the back door with the shotgun equipped. Use it to crown the backpack armoured with a Sparkshot, then take out the remaining, ideally saving fuel.
#50 Onwards. Try to lure zombie #50 (A Pale Head coming in the front door) to the back door. Run up the middle aisle, then spray some flames towards the backdoor. The exploding zombie there should take out himself plus two Pale Heads.
From here on in, it gets less predictable. Try to stretch out your health and conserve your ammo. Save your rockets for when you can take out a LOT! Rockets and exploding zombies kill through the shelves, so if you shoot a rocket in the middle aisle when the room is full of zombies you can kill a lot. Look out for the Red Herb guy coming in the front door at #88 it's around this time you can use a rocket to jump to #95 or #96 by firing near the counter. By that stage you should have a few shotgun shells, some fuel and some Uzi bullets to mop up.
Good luck, can't win this for you, but bad luck can ruin a perfect run. Keep at it, keep trying to stretch the health and ammo out and you WILL get it! Let me know how you got on in the comments!