I think the chop shop thinks that every Merc drivers are bloody rich or can afford it. One example is an engine similar to mine (16v), some of them were asking for a price close to 20k and average price was 12k. And they said it's because it's worth it. Yeah right it is!! technology for that engines is more than 20 years!! Biggest BS I've ever heard. But I finally bought mine for 5k after shopping around here and there.
But I have found many of the 104s around, besides being in the 124s it is also in the 140s, 202s, 129s and all the same. Many people in the US have put in the 104s in their 190e from different sources anyway. A C36 went into a 124 from a Merc article I've read, cool eh?
Anyways some shops were asking for 12k for the M103. But the point is different shops different prices. I found a V12 for 12k and to me that was worth it because of the high-end tech in it (unfortunately rats made a home in the engine). So it depends on where you look. If you ask me about the K, as compared to the 104s, the K engines are not that great. Yes it has good pick-up etc and hp could be around close to 200 but if you're talking about performance 104s are still better. The feel of a small displacement compared to a big displacement still varies despite the kompressor in the engines.