I tried to book via the site of a coach company for return travel (approx 200 miles each way). The website booking system was clunky and unclear and quoted me almost £160. I went to the bus station, where a very helpful assistant found cheap tickets on the same service at the same time and the cost was £80. I think that each coach has a number of cheap tickets and when they are gone, one is charged full price. The only thing this, that company does not say so on its website.