Easy Onion Soup Recipe- Vegan, Cheap, Gluten Free

What do you do when you want to feed a crowd tasty food, but you really don't want to be spending a lot of money? That is something my sister in law and I were discussing yesterday. We have our annual family reunion in a few days, and she and I, as the ones doing the cooking, were discussing how to feed so many people without breaking the bank.
I thought to do onion soup as an appetizer, since onion soup can be made for pennies!
I've shared a recipe for onion soup in the past, but it was more complicated than this, with more ingredients, and people weren't thrilled that it had wine in it, as it is too expensive for them (whereas I used my own homemade wine so that part was cheap for me).
Either way, this is the recipe I decided to cook up for the crowd, and I have to say, despite not having a million ingredients like the other one, it's pretty good. (My husband said it tasted like restaurant stuff, but I'll let you be the judge of that.)
The idea for this recipe came from an old neighbor we had, who made her onion soup with just soy sauce, mustard, onions, and water. I added a few more ingredients, but you can definitely see that that soup was my inspiration.
This is vegan and gluten free, but if you aren't vegan or gluten free, feel free to serve this with cheese and/or bread.

Easy Onion Soup Recipe- Vegan, Cheap, Gluten Free

Ingredients:
2-3 tablespoons oil (any non strongly flavored oil is fine, like coconut, sunflower, etc...)
4 large onions
3-5 teaspoons dijon mustard
7 tablespoons soy sauce (use gluten free soy sauce)
10 cups water
3 teaspoons salt
1 teaspoon garlic
1/8 teaspoon thyme (optional)

Instructions:
1. Slice your onions very thinly.

2. Heat up the oil in a pot, and add 1/4 of the sliced onion, and cook until starting to brown a little.

3. Add the rest of the onions and cook for 3-5 more minutes.

4. Add the rest of the ingredients and bring to a boil, adjusting the flavors to taste.

Are you a fan of onion soup? What do you put in yours? Does this look like a recipe you'd try? What do you make when you want to feed a crowd on a budget?