iBert child bicycle seat that attaches to the front post of your bike, so the child sits safely between you and your front handelbar.
These are $125 at Amazon, and even the mounting bar thingy is $44. Ours is an older model, though, and it's a bit dirty from being used by 2 kids and then stored in my bike shed for the past couple years.
I'd be happy with $25 for it if it's useful to you. I have the strap as well (not pictured).