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Though it won't give you values that you can actually sell the cards at, prices at a retailer like Troll and Toad will at least tell you which ones are more valuable. Real market value is typically the average price they've sold for on eBay (not what they're listed at, what they actually sold for at the end of the auction), after accounting for the outlier prices.
It's hard to really tell. Things like TGCPlayer are pretty good to check so you can get a rough ballpark value. Previously i had just used coolstuffinc.com to price check and then sold for a substantial amount under that price.