If you have recently bought or are thinking of buying a DVD don't get carried away. e Bay is a fantastic place to buy stuff, but not always the cheapest! I get most of my DVDs from e Bay and I pay around £2 to £3 for most. Sometimes DVDs attract higher prices, sometimes a lot higher. My advice is to check other sites first, such as HMV, Amazon or Play. there are many others. Brand new DVDs in the wrapper and delivered from £1.99 are available.
Look out when the title or description says 'rare' or 'deleted'. It is often not the case at all. For example, I want to get 'Red Dawn', a 1980's movie. Not very good really, but I like it and thought I'd add it to my collection. I was amazed to see that it attracted serious interest. I saw one go, 2nd hand, for £9 + £3 p&p. A quick check on the HMV site and I got a brand new copy, sealed and delivered for £5.99. Another example is 'Battle for Algiers'. £15 on HMV or Amazon, up to £35 on e Bay!!
Now as I said, e Bay is great, but given the choice and at the same price or cheaper I will always buy from an established retailer simply for the peace of mind. Delivery is always swift and guaranteed. I will never stop buying DVDs from e Bay though, but I will make sure I don't pay over the odds.