Tips on deciding to replace pump?

My pump has a new hum and sometimes it's very loud. I called the local pool store and they are saying it's likely I'll need to replace it for money on the order of 100s. However, for 88$ I can get a tech to come out and look at it. I was hoping someone might be able to advise me on what to look out for and how to make a decision about replacing it when the time comes. I can't afford to hemorrhage a lot of cash for the pool if I don't need to.

I don't know how old the pump is--it came w/the house 2 years ago. I have an above ground, chlorine, 28,000L pool.