I know the coords to a double spawner, a skele and a spider, and I'll be glad to sell them to you for way under 5k.
Honestly, Don't buy spawners.. People will almost always scam you somehow.. If they don't they will give you the spawner, and then kill you and take your stuff, and or use the fact that you use that location as a means to find you and kill you later. Regardless, if you want a spawner and want to be relatively safe, find one yourself, and you have much less chance of having something bad happen to you.. I would never buy spawners from anyone, no matter how much of a ... "Good deal" they make it seem. It's entirely too easy to find one :]
The thing i absolutely hate is people selling you illegal mob traps, that has happened to me and a spawner i almost bought i checked out and was illegal. I reported both. I might now even buy a spawner. AND THERE IS NO OTHER SPAWNER! :evil: :evil: :evil: