Yes, there are such critters as DVD-RWs. Just make sure to get a "-" type, not the "+" type.
Also, erasing the media involves using the Disk Utilities. Not a big problem, just slightly inconvenient, unless you select your hard drive or an external hard drive to erase by mistake, in which case you will probably use some words that your momma wouldn't be too happy to hear. (I speak as the "Voice of Experience" (VoE Tm) on THAT one!