Even if the amount of copies is low, it doesn't always have to mean that the item is rare. Take for instance the jukebox promotional copies of Firestarter or Breathe. There are only 500 copies of each, but both are still available for low prices. The same goes for these Baby's Got A Temper promotional records which are sold by XL-Recordings. The fact that XL-Recordings sells them themselves makes it even less rare since normally you can't buy them from them.
I've seen so many of these new XL-Recordings promotional copies for such low prices, that at the moment I wouldn't call it rare. Maybe in a year or so it will be more rare. But well, like I already mentioned, take a look at those more recent jukebox promotional copies. It's been years ago that they have been released and they aren't worth that much.
An original What Evil Lurks is worth more than one of those new Baby's Got A Temper promotional copies which are sold now by XL-Recordings, whereas of those original What Evil Lurks records there have been around 7000 made and of these new promotional copies 900 lets say.
How hard something is to get is how rare it is. The more are made, the easier it is to get most of the time. But if you take a look at the example above, you will see that this is not always the case. In Dutch we say 'what the idiot is willing to pay for it', that also raises the value. And of course, is an item wanted by the public?
(I hope my reply made sense ;)