Servers cost money, nothing can change that. But you could use a computer at home thats running all the time and then use a dynamic dns service (there are free ones) to access your home server from everywhere. That way you've got the electricity cost of an always running computer, so it's not entirely free either. Maybe use a sbc like raspberrypi, bananapi, odroid or the like, these are very efficient.

If you consider using a paid VPS instead, I can recommend contabo, since they are very affordable and work like a charm, e.g. the 200GB SSD variant for 4,50€/month: https://contabo.com/de/vps/