Cordon of Arrows is made for spell scrolls
Cordon of Arrows is an odd spell at first read, but it starts to make a lot more sense when it's scribed into spell scrolls.
Give your Ranger proficiency with Calligrapher's Tools or Arcana and at level 5 you can start scribing one CoA scroll for every 3 days of downtime, at a cost of 100 GP per scroll. Now, the amount of down time you'll get will vary by campaign and by DM, but 100 GP every three days isn't that much in Tier 2. As long as you're getting at least an average amount of treasure, you can probably afford to do this pretty consistently with whatever time you do have.
Keep this up over a long enough campaign, and sooner or later you'll find yourself facing a big fight in a location where you can get the enemy to come to you. This is when you get out your pile of CoA scrolls and start casting them, one after the other. Casting time is only one action per scroll, the spell doesn't require concentration, and by my reading of its description there's nothing to stop you piling all the arrows into the same 5 ft square so that they all go off at once. As long as the enemy shows up within 30 ft of that square within the next eight hours, you're all set. The arrows will fire on their own, so there's no in-combat action cost for you, their targeting ignores darkness and invisibility, there's no friendly fire, and if you know what you're going to be fighting you can even set the spell to only target the low-dex monsters. And none of this costs you a spell slot.
Of course, the results are more spectacular if you save up lots of scrolls, but you get a proportional benefit with smaller numbers too. Just use whatever you have with you when the opportunity presents itself.
Spell text for reference:
>CORDON OF ARROWS (2nd Level, Action, Touch range, VSM, 8 hour duration)
You touch up to four nonmagical Arrows or Bolts and plant them in the ground in your space. Until the spell ends, the ammunition can’t be physically uprooted, and whenever a creature other than you enters a space within 30 feet of the ammunition for the first time on a turn or ends its turn there, one piece of ammunition flies up to strike it. The creature must succeed on a Dexterity saving throw or take 2d4 Piercing damage. The piece of ammunition is then destroyed. The spell ends when none of the ammunition remains planted in the ground.
When you cast this spell, you can designate any creatures you choose, and the spell ignores them.
Using a Higher-Level Spell Slot. The amount of ammunition that can be affected increases by two for each spell slot level above 2.