Homemade vinaigrette is easy to make and economical too. And all you have to do is remember this ratio to make vinaigrette any time: 1:4. That's 1 part acid (lemon, lime, vinegar, etc.) to 4 parts olive oil. You can stop right there, or you can then add a little mustard (for flavor and to help the vinaigrette emulsify), and salt and pepper. If you want to go further, you could add some garlic and/or shallots. The sky's the limit, or you can be a minimalist.
I am usually a lemon, olive oil, mustard, salt and pepper vinaigrette kind of gal.
With the 1:4 ratio, you can make a little as a you want (e.g., a tsp. of acid to 4 tsp. olive oil) or a huge vat of a salad dressing. If you want to cut the oil, you could go to a 1:3 ratio, but you might have to add a little sugar to cut the acidity. If you use a cheap balsamic vinegar, which contains a lot of sugar, the 1:3 or even 1:2 ratio will work just fine.