Its probably worth the 100 dollars but don't think its worth the effort. It looks like a 10 gallon tank so about the only thing you are going to gain is a skimmer and maybe filter sock or some other mechanical filtration. See if you can talk him into selling just the skimmer and return pump. Then get a 20 gallon long (1$ a gallon at Petco) and a DIY baffle kit (I believe a vendor on this site sells them). this way you will have more room for more stuff (refugium, reactors, ect).