#1
im looking to get a 12 string soon and i was wondering the best kind for about $500
#2
I have one and it cost me £200, approx $370 and I love it. It's an Ashton Sl29. It sounds incredible and looks the part too. It has a built in tuner and is electro-acoustic. It holds its tuning very well as well.

http://www.hartnollguitars.co.uk/subs/image-sizing.asp?Path=Acoustic-Guitars/SL2912CEQ-TSB.jpg&Width=137.614678899083&Height=375
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#3
You really have to watch the cheaper ones. A lot of them can't handle the string tension and the neck will begin to warp/twist over time. Most folks recommend using drop tuning on the el cheapos. Now, on an expensive Martin, Taylor, Takamine or any other high-end 12-string, you can get away with standard tuning, since the guitar is built to high standards.
#4
Look at Seagulls. Got mine for $470 and I love it.
Seagull Coastline S12 Cedar 12-string
Epiphone EJ-200 (natural)