How to fix belt squeak on 2004 ford explorer?

2004 ford explorer started squeaking from time to time only when the A/C was turned on about 8 months ago. And looking online it was recommended that a cheap and probable problem was the idler pulley and the belt itself. So I replaced those and the squeak stopped for about a week or two then came back. Well over time the problem has gotten worse and it now squeaks upon cranking and accelerating whether the A/C is on or not. I also read that a problem could be that when an alternator is going out it will squeak, so today that finally went out and I had the opportunity to replace it. And the squeak is still there. I'm at my wits end with this and don't have the time, money, or patience to deal with (usually) dishonest mechanics who want to charge an arm and a leg. Anyone have any advice/tips? It would be greatly appreciated.

Either the belt is saturated with oil/coolant, something leaking on top of it, or its not tight enough, if you have an automatic belt tensioner (tensioner with spring in it) the tensioner may be going out.

never really seen an alternator going out make belt squeal, unless it was a diesel truck

I would look at the belt tensioner

Start the engine and spray some Blue Coral carpet and upholstery cleaner on the belt. If it stops squealing, you've got oil, anti-freeze, or grease on your belt. Change the belt. If it keeps squealing after you spray it, it's a pulley and not the belt. Either way, I would change the belt while I was there.