Tape ins at the nape hold water way longer than the top sections, so I dry just that part first.

Wedging rubber into a window track is just hiding the real problem, which is that the sash or the balances are worn out and the window no longer seals right. That gap you plugged is also where air and water get in, so you may have traded a rattle for a draft, a stuck window, or rot down the line. The $200 quote probably covered new balances and a proper seal, which actually fixes the cause instead of muffling the symptom.

Sounds like a lot of work to save 41 bucks when your neighbor's bill barely moved, so maybe the real problem is your place leaking air or something. Water heaters pull way more power than an AC anyway, you'd be taking cold showers for like 10 dollars a month.