Squeaky Motor Mount?

2003 Kenworth W900L, C15 cat. Got a loud squeak I've been hunting for several months if not a year. I've posted another thread about the hood shaking and I was thinking the squeak was a result from hood shake. I've pretty much ruled that out. Squeak from what I can tell sounds like it's coming from around the firewall down around my feet on drivers side. I've been over it a lot and can't find anything loose or moving and can't find anywhere that looks to be rubbing that I haven't greased or adjusted. Any of you guys ever have a rear motor mount go bad that squeaked?

 

Only when rolling. Especially when slowly moving around on rough lots and on rough roads. It will stop with just the slightest turn of the steering to right. Gets worse when steering turned to left. I know for sure the drivers side rear mount needs replacing. Just wondering if it could possibly be what's causing the squeak. I'm thinking maybe the turning of the steering wheel is possibly flexing the frame rail just enough the stop the squeak or make it worse in the other direction.

 

Anyone got an idea of a ballpark price for the rear and front mounts/bushings?

 

Stack bushings squeak at times but they are for sure not what I'm hearing now.

Are the rear motor mounts a huge job to change? Fronts look pretty simple.