Fixed today. S..., it was harder than I'd expected and took ~4-4.5 hours. If someone asked me for how much I'm ready to do it again I would say that not less than US$ 150.
After all of this I've thought "do I really needed it?" coz I was passing 5 winters without bottom heater, only with back. For why I did it now - I don't know Anyway, everything is working now.