From Ho Chi Minh City, it is a 5 hour bus to Mui Ne. Book Phuong Trang or Mai Linh or any open bus tour on Pham Ngu Lao Street and the price is more or less the same ($4.5). You can request for a stop at your hotel to avoid extra-transfer.
From Mui Ne, there are buses to Da Lat (4 hours), Nha Trang (4 hours) and destinations in between these sites. Bus tickets are for sale at your hotel or travel agency along the coast.