Buying a used body kit off of eBay is a no-no.
As for a "cheap body kit" -- the term doesn't really exist. Especially for Caddies. That said, however, I was under the impression that the Erebuni kit goes for about $1k? (I found it here (after a Google search, not recommending this site in any way)
http://www.autotoyaz.com/erboki92case.html for $900.00). If $1000.00 is your total budget including installation, however... good luck finding a suitable kit.
I wouldn't recommend the WickeD kit as it looks terrible.
In fact, the only kit that I find add positive aesthetic value to the STS is the evolution one -- and it runs about $2k. (I also haven't found a person able to figure out how to order from the company internationally, so there's another road block.)
Anyway, sorry for the somewhat bad news.
Do you have a link for the Wicked kit or a price? I'm curious where you saw it
EDIT: There was this weird imported Kung Fu movie I saw a while back about an alien space ship. It had ninjas and transforming airplanes. It had a nice STS with the evolution body kit. I think the Caddy in "Equilibrium" had a kit, too. :eek2: