How much do Superman,Spiderman and X-men comics go for?

My sister has ALOT of marvle comics and she wants to sell them she has over 100 mostly x-men and she has a few spider man and a lot of Superman...even the comic that was suposed to be the last superman comic...but she isn't sure how much they normally go for..where can i get her that kind of information..or better...where can i sell them for her??..How much do Superman,Spiderman and X-men comics go for?Ok first of all it matters on how old they are. The older usually means the more expensive. Also if the issue is very famous then it will be expensive. Try buying a magazine called Wizard and on the back it has a list of comics and how much they are worth. If not then just try bringing them to a comic store and ask how much they would buy them from you. And if you dont want to do that, put it on ebay or craigslist. eBay you need to pay money to put it on, but craigslist you dont. Also Superman isnt Marvel its DC, very different.