I made a rope but it was a pain.
I bought 4 Manila rope lengths from the hardware store (can't remember the length) - I think they were 1/2 inch in diameter. I looked up a video for braiding a good climbing rope, and then had my wife help me braid it. It's pretty much a 2 person job just to keep the loose ends untangled.
It ended up not being thick enough for climbing comfortably, but my kids have fun playing with it. I'd aim for at least 3" thick if I had to do it over again. I do climb it a little, but it tears up my hands.
Edit: I think I spent less than $15 overall for a rope that would have cost more than $100. Sucker is pretty long.