Plumber used 50 ft snake at the base of toilet, all seemed well but less than two days later, when runnig sink water, noticed toilet bubbling. The next day, feces acked up into the tub when we flushed the toilet. Help please, I can't afford plumber again. Can I do this myself?

Why not call the plumber back and inform him he missed the clog. As toiof you can do this yourself the answer is yes you can. But first let's be sure exactly where the problem is. Are you on city sewer on a septic tank? Locate and open up the house clean out and cycle the washer. If the line fills up then snake from the clean out. If not then the blockage's local.
Rent a sewer snake and you have two places that you can snake from.
1) You can pull the toilet and snake from there,**OR**
2) You can snake from the lavatory roof vent. Put out enough snake to reach the base and 20 feet more. Good luck, Tom