I am not sure of the bus services available at Le Coco Beach, but knowing Trou aux Biches there is no direct bus line that I know of. You would most likely have to catch a bus to Goodlands and change there for Trou aux Biches on the Triolet Bus Service.
I've found Goodlands fairly good for shopping and they have market days. Food is on different days to clothing, etc and prices are generally cheaper than you find in Port Louis. Goodlands is worth having a walk through to check out the shops if visiting Mauritius.
Taxi may cost more but may be an option, depending on your time and budget. I know a bus ride can be a good way to see an area as they don't always take the direct route and sometimes you strike up conversations with people.