There are four total mounts on this vehicle:
Front engine mount (near drive belts) Rear transmission mount (below battery area)
Front roll stop mount (near center bottom of radiator)
Rear roll stop mount (near center lower firewall area)
The engine and transmission mounts are both about $125, and the two roll stop mounts are both about $70. You can purchase these aftermarket (NAPA, Autozone, etc) for a decent savings over Mitsubishi prices of course. Additionally, if you prefer genuine parts, you can order them from MentorMitsubishi.com, they sell genuine parts for 25% off list price.
Installation time is just a bit over 3 hours to replace all three (figure about $270), however realistically it does not take this long to change them. Replacement of two of the mounts can be done yourself fairly easily, and the other two are a bit more difficult, but doable for a seasoned DIY person.
Starting with the easiest:
To replace the front roll stop mount, loosen the cross bolt in the mount, then remove the four bolts holding the lower front/rear crossmember to the frame. Slide the cross bolt out and drop the crossmember out of the car, and unbolt the roll stop mount from the crossmember and install the new one.
To replace the front engine mount, put a jack and a block of wood under the oil pan and support the engine. Remove the bolts holding the mount to the frame and to the engine, then remove the mount and install the new one.
For the more difficult ones:
To remove the transmission mount, put a jack and block of wood under the transmission to support it. Remove the intake hose, battery, and battery support bracket. Remove the bolts/nuts holding the mount to the frame and the transmission then remove the mount and install the new one.
To remove the rear roll stop mount... you really need a vehicle hoist for this one, as this is very difficult to do on the ground. You will need to remove the cross bolt by putting a wrench on the right hand side and accessing the left hand side through multiple extensions through the wheel well. Remove the mounting bolts to the K-member and ... this is the fun part... fish the mount out of the engine bay. The mount will only come out if it is negotiated around everything in the way, which will take numerous flips and turns to find a smooth way out. This is why it is good to have the vehicle well over head so you can comfortably move and view it's position.