How much to replace struts and how do I know if I need them or not?

Depends on labor rates in your area, but you can test to see if you need them. Look at them and see if they are leaking. Push down once on the bumper at each corner of the vehicle. If the vehicle bounces more than once before stopping, you need struts.

What you should do is buy some really good elantra struts from shark racing, they are easy to apply to your car and they are probably the best pair of rear and front struts you can find specially for an elantra. Just go to www.sharkracing.com and choose the year of your elantra and they will show you all the parts that they sell for the elantra.they have some good stuff you should look at them.