I put one of these in because I didn’t want to mess with propane or natural gas. I really didn’t even notice a bump in my electric bill but I did insulate the shit out of my garage. I keep it at 50 degrees.
https://www.amazon.com/dp/B00HS8FZAC?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_1&th=1