As far as I can remember, my first LP purchase was this:
http://www.discogs.com/release/2642237
I bought it because I believed the pirate radio advertising that told me that this was going to be all the rage, so that I could be one up on my friends. Of course, nobody else ever even heard of it!
My first vinyl LP was Well Respected Kinks. 12 shillings and 6 pence. I had it for years and played it often. I was gutted when my 7 year old, back in 1978 played frisbies with it.