You know my feeling Jeanette. I don't believe that you need both as they do almost if not exactly the same thing. I think the only difference is the dry coat you can put on when wet and blow dry as in the shine coat only goes on a dry coat. I also put the dry coat on a dry coat and works just as well. Flattens it down and nice shine. I haven't actually tried the shine coat as never felt the need to really as more than happy with the dry coat. The only thing I'll say against it is the elastic round the head peace was a little tight, but I just cut that out and it's always worked fab. Dru looks a different dog when he's had his on and has always brought Tally's coat up lovely. I've never looked into prices either as the dry coat was a recommendation to me and I've never looked back. I say go for the cheaper as it's just as good, but of course it's your choice as you need to be happy with whichever you choose.
