Got a BMW 325 on the go but more importantly a Volvo 340 1.7 I have skids easily in the wet standard with a welder lol. just about any rwd will give you some slideys with a welded diff.
Also I'd be careful commenting on how you would hate to have another guys car. Kind of like making fun of a guys girlfriend when you don't have one yourself. Atleast he's got something that will drift.
Depends on the differential that he bought. Typically a 1.8 Torsen LSD with halfshafts and driveshaft runs about $700 to $1,000. Maybe a couple hundred more for a Mazdaspeed system. (stronger all around) Of course that is if you are swapping it into a 1.6 car.
If the car is already a 1.8, then he'll just need the differential itself. So knock off maybe $200 to $300 from that price.
Aftermarket LSD's typically run on average around $1,000.