As Chuck stated what Jaguar are you looking to buy. A series one or two E-TYPE soft top in a good driving condition could set you back $50,000/$90,000. A fully restored example to Concours condition, well, the sky's the limit up to $200,000. A series three ( V12) much less money and any of the coupe models slightly less again, but gaining in value.
For my money I would purchase a later model XK8 soft top, the years from 2003 to 2007 would be a good place to start. These models would be kind on your wallet and can be bought from $15,000 to $25,000 or more depending on condition. An earlier XK8 1998/2002 DEPENDING ON CONDITION, can be purchased for $9,000/ $15,000
Just some food for thought
Good luck
David