I'm not 100% sure, but I think all listings in the media category are only 5c each in a store, so it might be a good option for you, as you can list each LP for 30 days for this price. An auction listing will cost you 50c (up to a start price of $19.99)

I woud think your best bet may be to try a few of the free auction listings first to  "learn the ropes" so to speak...

And good luck!