timing chain going?

[Rutherford]

Well I am at 273,000 miles on my 2008 Yaris and she has developed a strange rattling noise which comes and goes. I used my old timer way of figuring where it is coming from (piece of hose and my ear) and it seems to be coming from behind the timing chain cover. So this is something I am not going to try and do myself probably and I imagine if it is what I think it is it will require several parts besides the chain. Two questions come to mind here for me.
1. Dealership cost - I live in a rural area so my local dealer charges what I would call a normal charge, usually won't rack you over the coals but he gets what the book probably tells him he can.
2. How long will she go before she dies and if she dies will there be added cost for letting her go that long.

Thought the transmission would die first but it seems to be hanging in there after a fluid change.

She still runs great after being the trail rated Yaris versionand the funny thing is I just moved off the mountain with gravel road that beat her to death all these years. She was suppose to retire down here in the flats

Could it be anything else from that area of the engine?