The most important point I can transmit is perspective. Doing a complete timing chain head job is about half the labor of a complete overhaul. The parts are much smaller percentage of the total overhaul in the timing chain repair. If I charged $4k for the first instance I would thus have to charge probably $9k for the second.
We charge 25 hours labor to do the cylinder head/timing chain overhaul (without front cover removal), 35 hours with it and about 55 hours for a complete overhaul. Our labor rate is $65 per hour. This means that we will do the first job for around $2500 and an overhaul for around $6k. We have only done a couple aluminum block engines as they just never need the cylinders redone. As such we have done hundreds of timing chain repairs and have never done a complete motor for that reason. The two that we did were overheated to destruction and they were years ago before the price of used motors dropped.
It seems you are answering your own question about the $4k estimate if you think you can save money by doing 60% more work.
The real answer to your dilemma is to either scrap the car or repair whats broke. It won't need a complete overhaul which should naturally cost twice what an upper end overhaul will. A used motor will have the same deficiencies as your old motor. In the end you will wind up with a new chain system and a new valve guide system (something that needs doing every 200k anyway). The bottom end doesn't need anything. If your areas economy has a $4k tag on this work then old cars will be cheap. Unfortunately the catalog companies can't sell you a chain overhaul in a box.
Bosch Master, ASE Master, L1
33 years MB technician