Recommend a RWD Differential

Hello, all.

I have a project car that is being built from the ground-up. The rear axle will be a de-dion design (the differential will therefore be mounted on the chassis, reducing unsprung weight).

Most likely, it will be mated to a 4AG-E engine/T50 transmission. Car will be very light (estimated 600kg).

What's a good RWD Differential to use?

Criteria:

1. Locally/easily available, and therefore relatively inexpensive (i.e., pls don't point me to super-duper differential from an EVO that would cost me an arm and two legs);
2. Can take power from 4AG-E
3. The lighter the better
4. LSD a big plus, but not required
5. Easily serviceable (parts availability/compatibility) in case it goes bonkers.

What RWD differential should I be on the lookout for? And can you point me in general directions where I can find such a beast? And finally, how much do you think it would be?

Thanks!