I use 8 oz. flip-tip bottles. They're inexpensive, easy to find, and the top does double duty as a spot applicator.

I buy them four at a time. They cost forty-seven cents a piece. Their 2-3 business day shipping was very reasonable for where I live (Maryland).

Plastic Squeeze Bottle w/ Flip top Bulk, 8oz |Specialty Bottle

Note: they make 2 and 4 oz. bottles, too.