Is it just squeeling or do you notice it takes more effort to turn the wheel ? When you turn the wheel does the squeel change pitch ? If so then yeah it's the pump for sure. Does the sound change with the engine revs ? If it's not the PS pump then maybe the water pump, a dying air pump, probably not the alt but maybe just a bad idler pulley. The easiest way to start narrowing it down is to see what it does when you turn the wheel back & forth while stopped. Checking the fluid level is usually a dead giveaway too. Like JSM said you can do a saginaw conversion or just a straight out swap, either way you can get the pump from Snake Rd for prob $30-$40, maybe half that if you pull it yourself. If you wanna take a run down there lemme know since I need to go down & look for an inspection plate for my AOD and I may have to hit them up for some flywheel bolts & some other misc pieces. If you want swing by & we'll take a look at it & see what's what. I'll shoot you a PM w/my cell.
Just for the sake of comparison, Jeff's gets $100 for a rebuilt Ford PS pump:
http://broncograveyard.com/bronco/i-32811_...mp__rebuilt.htm
and $195 for a rebuilt Saginaw pump:
http://broncograveyard.com/bronco/i-20975_...pump_option.htm
You can also get a rebuild kit for your existing pump as well, last time I priced one I think they ran about $15. A good option is to pickup a used pump & swap it in then rebuild the one you took out, swap the rebuilt pump back in then put the used one on the shelf as a spare & rebuild it when the football season ends and life seems to have no purpose.