Are there any reasonable substitutions for lemon juice?
When you find cheap lemons, buy a lot.  Squeeze half a lemon in each of the cavities of an ice tray.  Freeze.  Within a day, remove the frozen slivers from the tray to a ziploc bag in the freezer. You now have measured units of fresh lemon juice you may use for cooking and will keep for months.  The frozen lemons are a bit less acid than fresh juice, but full of flavor.  You can do the same with limes.