Motor mounts $$$$$

I have a 1993 Mercury Topaz, 4 cyl, 66,000 miles. I am the original owner and have driven my "baby" just around town. Almost two years ago I noticed a slight vibration when idling (worked fine when driving) so I took it to a mechanic and he replaced one motor mount. I also had tune up, bought two cheap tires, oil and lube, and a new battery. Don't have the paperwork so I can't see the itemized cost of the motor mount but the total amount was $700.00. About two months ago it started vibrating again and this time it rocks when idling. Here's my question. How many motor mounts does this car have and how much would it cost to replace them (minus the one I already had done.) I love my car and had hoped to get another 2 to 3 years with it. Note: If anyone could help me my e-mail is [email protected]