There are options depending on what you call "cheap". Ask if someone in the local flying club has a suitable charger for sale. Or, for about $130 you can get a new Hitec X2 AC Plus Black Edition 200W 10A 6S Battery Charger / Discharger. It runs on both 120 volt AC in the house and 11 to 18 volt DC out in the field. This will charge two batteries at once. A deep cycle marine battery (trolling motor battery) is sufficient to recharge your small size (2S-550mah) batteries for a full day of flying. Yes, you could make a jumper cable to attach to the car battery, but never, never, never charge a lipo battery inside or near your car due to the potential fire hazard. The last option is to get a parallel charging/balance board. IF you are charging identical batteries (brand, size, cell count, condition) a paraboard will let you charge 1 to 4 identical batteries at the same time. Take a look at Buddy RC at this kink: https://www.buddyrc.com/collections/paraboard