There is also the issue of use and reuse. A lot of the basic masks should be single use, so every time you go out you use a new one. 60 million people cannot be supplied with these. A resuable mask that you can wash every day is a better option and if I had to go out and I was in an 'at risk' group I would be taking every precaution.
Its basically containing the volume of infected stuff in a cough or sneeze, but if you have one on and someone coughs or sneezes in your direction you are still going to get the stuff on you.
Some bookies may not, check the rules. B365, do or you can take the USA pool prices. If you watch the live feed you can get an idea of where the value is. There was a fav last night 8/5 in USA but 6/5 here.