Need a replacement suggestion for the IAC valve. Checking several parts stores there are about 10 different mfg with prices from $28 to $100. The motorcraft is $92 at O'reilly which I assume is the oem but if the $28 Standard is of the same quality, performance and longevity it would be a nice savings. Then, there are the Duralast and BWD for around $50.
Have you tried cleaning it? As long as the motor in the IAC functions you don't typically have to replace them. Depending on the design, I usually remove it from the engine, hose it clean with carb cleaner or or the like, then juice it up with wd40. I try to work the piston with a small screwdriver to just to get if freed up and some lube around it.
It's basically a piston with a linear actuator, it's a simple enough design you could get away with the cheap ones.
Another free thing to do for haunting idles is to take the throttle body off and wipe the gunk off behind the throttle plate. Open the plate by hand and get as much off as you can. This will cause haunting idle too.
Another thing to check is vacuum leaks. Once it starts getting close to level idle, spray starting fluid over the vacuum lines and around intake manifold. If the engine revs up, you sprayed near a leak.
If after all this, it still doesn't act right, it may be time to break down and buy parts. No sense throwing money at it until you take care of the free stuff first though.