If you don't want to spend money on it, than probably it might be better if you just leave it as a single chainring in the front and just peddle harder when you come to a hill. That way you can put your budget into doing a proper job of rebuilding, replacing or upgrading the wheels, and brake parts or new cables and rubber.

After you get it working smoothly. Then down the road or next year you can look at putting in an extra chainring. But for now you'll have one less thing to worry about.