$50 to $75 an hour is too low for a shop rate in my experience. Most all the shops in the greater Seattle/Tacoma area were charging between $120 and $150 an hour. The mechanics that worked there got between $18 and $30 an hour. When I started my last business I was charging $125 an hour shop rate. When you consider I paid for all the equipment, rent, gas, electric, water and all the miscellaneous costs of the business plus the $30/hr for my employees plus their benefit package I ended up with a net profit of about 5%. I was kept busy because we had a reputation for good quality and we kept that reputation intact.
My employees were making $240/day plus holidays, vacation time, sick leave and medical and I got about $150 - $160/day as the owner after all the bills. My net worth was considered higher because I owned the equipment and supplies but that didn't pay the mortgage or my bills at home.