Silver Surfer Book Bag

What is a fair price to pay for a box of comics?
I understand that you will not be able to answer that question precisely because this would require to know the status and title of the comic. But this Friday will not be a garage sale in vicinity and that the ad mentions there are 10 "long" boxes of comics for sale. For those of you who do not know "box" time is about 27 inches long and has about 225 comics. The ad says: "Comics (over 10 boxes of long integer) Late 80's Mid-90's Marvel and all related titles Image Spiderman X-Men Silver Surfer titles and other random wonder all the initial image: Spawn, Youngblood, Savage Dragon, etc. "I am also informed that they are all provided near-mint/mint and are all bagged. Supposing I wanted to buy these, with the idea to slowly, over time, re-sell them, what do you think is more than I want to pay them? What would be a steal, and it would be too much? (A fair price would be then probably in the middle.) Again, the best answer possible.
For the titles you mentioned, and years, and the amount. I do not would give more than $ 80, not less than $ 50. I need to know the feedback of knowing exactly wortheyness.
Silver Surfer Comic Book Collection