I am afraid by the sounds of it you have a standard Darth Vader as as he is missing the tip it is likely that he is worth no more than about £5.00.
The ones selling for $2000.00 are Double Telescopic Darth Vaders - and their lightsabres are made up of two peices, the stem and then a long thin peice that fits inside.
Post up a pic of the lightsabre just to check but I am afraid you are not sat on a gold mine