Probably depends on if they are cheap rubber jobs or hydraulic year and model may help, or google to find out, I had one replaced on an old Saab for about £75, replaced a couple on a fiesta they were about £3:50 each.

Shouldn't be too hard to do yourself if you are reasonably competent with spanners etc.

You might find there is a 'performance' mount (harder compound to reduce engine & gearbox movement with higher power outputs - more noise and harshness through car) available from an aftermarket supplier cheaper than the genuine item.

Just a thought.