I think I'd take a pad and paper and make a list of all the items that come into contact with the belts. ie-alternator, water pump, tensioner, power steering pump, crankshaft...
then, take that list to the parts store, or look them up on Rock-Auto.com and start with the cheapest one.
I agree with Tire-Iron...if it has an automatic tensioner then replace that first. If there is one there, it sounds like the internal spring mechanism is old and not up to snuff anymore.
You know, just to make sure it is the belt, you could purchase some belt dressing. This is a spray that you spray on the back of the belt (while on the vehicle) that makes it sticky and less likely to squeal. If that doesn't lessen the problem then you may have an issue with one of the accessories bearings wearing out.
Just a thought.
1997 Ranger XLT Stepside - 2000 2.5L Engine - Cayman Green - Actually it's running pretty good after new plugs, coils, plug wires, pvc valve and Injectors!!! Runs like a champ!
So, I'll open a homebrew play some Fantasy Football