Here's how I solved that problem.
1. Buy a pair of silicone ice cube trays. These make getting the frozen juice out SO much easier!
2. Buy a bag of lemons from Costco. They were $7.49 for around 16 lemons. That's about $0.45 a lemon - cheaper than my grocery store, for sure. I actually think they're out of season right now and are even cheaper other times of the year.
3. Get juicing. My ice cube trays make cubes of about 2 tablespoons each. A lemon fills 2 cubes. Good to know for recipes.
4. Because the silicone trays are flexible, I put them on a cookie sheet and carefully slide them into the freezer.
5. When they're frozen, just pop them out and store them in a baggie (or other container) in the freezer, ready to be whipped out when needed in a recipe.
I also do this with limes.