Maybe meters? I have a 35 foot HDMI cable so that's just over 10. I see 50 foot HDMI cables so that length is out there. Try to keep it on the shorter side.

As to coax, it is not usable due to differences in HDMI signaling and frequencies. Since that's a dead end, direct your efforts to a longer length HDMI cable. Here they don't cost much. is about 25 bucks to my mailbox.