I have a 2004 Isuzu Rodeo with 40,000 miles with lifter noise. I have been told to get rid of it quickly before it gets louder/worse. From what I understand Isuzu is known for loud engines and also the ticking is common. What will happen to my engine if this problem goes untreated? What are some possible fixes that aren't expensive?

lifter tick is common on the 93-97 3.2L isuzu's, but not on the +98.

I would start with a half can of sea foam in your oil. Drive it for 30 minutes and then dump the oil. the sea foam will help to clean up the lifters.