I'll have to explain a little for my collection...
I have only bought 2004 trilogy from retail and the only reason I'm keeping it is the extra disc. THX and SEs were bought to me as a gift. THX was the first one I ever owned so I had to get it. And at that time I thought the SEs were "cool" so wanted them, too.
All others were bought second handed. Other SE trilogy I bought for 50 cents. I don't remember how much the third one cost but it wasn't much. 2006 DVD tin box was 30 euros, second handed. Cheapest and the only one I've ever seen on sale here. Executor box was the most expensive but I'm keeping it for the cool extras. And all the rental versions are just because I'm a collector, they're the first ones and they are a piece of SW history.