The whole car? Nobody can tell you that without knowing the mileage, condition etc... 100k mileage 96-98 cars in good shape are in the $2500-$4k range. If it has like 250k on the body or something it'll be worth less.
Trans itself if its a stock rebuild by a known shop and you have all receipts is $500-$800. If you don't have receipts then any competent buyer has to assume its original.
2000 Mustang GT Steeda #0048
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.