I'm driving an '89 740 wagon that has 148K miles. I bought it with 120K miles, and have a feeling in my gut that its time to replace the timing chain, lest I destroy my engine. I'm wondering what the ballpark price should be on a job like this...it seems that every time I need to do something it's either $250 or $750, rarely more yet rarely less... I'd appreciate any guidance you have for this newbie.

Thanks.