try gocollect.com where's there's a free price guide for slabbed comics based on grade level. Not every comic may show associated grades (depending on #sales for that particular grade).It's always fun to look!
mycomicshop.com doesn't have a price guide but they sell a lot of slabbed comics so that is another free resource. Of course there's Ebay sold listings
You need to factor in shipping costs, to CGC & back (if you don't go thru a LCS), plus grading fees, plus any fees charged by a service if you intened to put them up for sale (Ebay or other auction houses),Paypal etc and compare that that against a poss selling price for the grade you'd expect. There's a "Buddy Can you spare a grade" forum where you can get opinions on the condition of the comic. A lot of times it's prob not worth the expense to get it graded once you factor in all of that
There's also a selling forum here which has the advantage of no fees like Ebay has - though it may help to buildup an "online reputation" here fiirst
good luck!