Aug pg. 126 says that two grades of cloned limbs and organs are available - type O and cultured. It says that type O can be acquired in a matter of days from a warehouse somewhere, while cultured has to be grown over time, or grown ahead of time and stored against need for the individual patient.

Neither type costs Essence.

Neither type can be grown any quicker, although type Os can be bought off the shelf.

Cultured is more expensive.

Why would anyone want cultured transplants?

And where does the market in second hand parts fit into this?

Well the role of secondhand parts is easy- they would be cheeper than both legal options.

As far as why anyone would want non-cultured transplants, the only reason I can think of is so that the corp or street doc you are getting the transplant from doesn't have access to your DNA. Of coarse by that logic what is to stop them from taking your blood while you are under anesthesia right?

So I guess I don't know..

If you want to give it some value, give the type-o a higher rejection rate - maybe up the number of successes necessary for it to take?

The biggest thing is this: Cultured is cloned from your own DNA. Once implanted, your body will recognize it as it's own, and there's nearly zero chance for rejection. Type O is basically what we have modern day, and the chance for rejection is reasonably low, but some people are forced to take immunosuppressents for the rest of their lives, just to keep their new organ working. That leaves them at risk to other forms of illness, because their own immune system isn't working at top notch.

Second-had would be even more of a chance of rejection, but would be significantly cheaper.

well... we always played it that the magically inclined HAD to get vatgrown, due to mixing up other dna with their own would chance essence loss at least from a magical standpoint. the magic stat would still take the essence hit even though the actual essence wouldnt.

There's also the psychological angle to look at. Type-O replacements might work, but they're not "yours". Or they might be the wrong color, size, or shape. No doubt they try to match them as closely as they can, but we are talking the mass market, where 'close enough' is usually considered 'good enough' (See Also: horseshoes, hand grenades). Or how do you really know it's a new Type-O implant? They could have gotten that thing from anywhere - maybe the last guy it fell off of. Not like you'd know the difference just by looking.

And even if a particular recipient isn't hung up on any of that - having a mis-matched limb is an distinctive feature that's not easy to get rid of.

We also play that magicians need cultured replacements to avoid any problems with magic. Also, I think PC's with bio-rejection have to have it too (but that could be a house rule).

Besides any psychological preferences, cultured transplants are required for certain types of organ replacements (anything requiring heavy neurological wiring); Type-O just won't do.