I've been told that my valve cover gasket needs to be replaced. They quoted me at around 250-300 dollars. For a gasket, that sounds ridiculous. How hard is it to actually do?

Also, whenever my car is parked for say, more than an hour, when I start it up. Put my foot on the brake, shift into reverse, and then release the e-brake. Whenever I let my foot off of the brake pedal and start going backwards it makes a fairly loud multiple popping sound.

Can someone please help me out? I'm hoping its not too big of problem.

Thanks again guys.

I changed my valve cover gaskets some weeks ago and they were around 30 usd each

How much time did it take you?