Well to even have chance to help you we will need to know the year your vehicle was made and what engine it has in it.
If you in fact have a code for the timing chain at only 70K it is indicative of some other problem causing premature wear to the timing chain or guides or tensioner.
This may require immediate attention if you do not intend on replacing the entire engine.
Meaning this is not something to take lightly.
The very first thing I suggest is confirm what code you really have.
Then come back here with that code and give us the year of your car and engine size.
$2400 is an outrageous price for a timing chain and if it is found to be what is really wrong with your car I would suggest getting an itemized estimate from the dealer whom gave you the original quote.
Then take the vehicle to a few other trust worthy knowledgeable shops for their estimates.
Cheaper is not always the best in a case like this yet, I would for sure want to know I wasn't being taken advantage of.
Has this engine suffered from poor preventative maintenance or extended runs on the oil and filter?
Have you had any other work done to this engine that you know of that could have led to this engine getting opened up?
One thing I cannot help you with is TSBs ( Technical service Bulletins )
I would make sure to find out if there are any TSBs related to the engine oiling system or timing chain.
I may be able to snoop around and find some data on this yet the best source that I know of is Alldata Diy.
Alldata is not a free subscription you would have to pay for it yet I could dig up the discount code I provided in a earlier thread.
If you call up your local Dealer and ask the service writer to look it up for you they should inform you of any relevant TSBs as long as they have your
VIN
They will not give you the entire service bulletin over the phone but if you went there they may print it out for you.