Take it slow and buy things as you need them. You don't need a computer, especially right away. The shorts? See how far you start riding. Could be you can get by with what you're wearing until the distance is such that you are uncomfortable. Check with local cycling clubs to see if there are swap meets around where you are.

You need gloves, a helmet, a multi-tool, tire levers, and tubes/patch kit. Oh and you need a pump. After that, just see how far you go with it!

I've seen bikes listed for very reasonably. There was somebody in Washington from TE who had a whole bunch of bikes she was selling for about $100/ea +/-.

You can do it