I was working at a mom and pop shop, and we used a saas web application for managing online shipping. For funzies I cobbled together some python that would poll

I was working at a mom and pop shop, and we used a saas web application for managing online shipping. For funzies I cobbled together some python that would poll a usb scale upon http request which would get called from a button on the web app injected by a greasemonkey script and fill out the lb and oz fields with the weight. When I got it working I was so excited that I immediately opened up their live chat and asked support if it'd be something they were interested in. They were a small operation and it ended up being the businesses owner who was on the other side. After a few emails back and forth we agreed on $3500 (plus our shop would get to use their app for free) in exchange for windows and mac versions of the code. Oh man, now was I really excited. $3.5k for a couple weekends of work, I've hit the big time! Later they sold to stamps.com for $50 million. I've since learned to charge more and to better estimate my time.