Maybe even more, possibly up to 400. They are in good condition.
None of the answers I’ve read so far are very informative.
I own more than 12,000 comic books. A photo of some of them can be found here:
http://www.edcollins.com/comic-books.htm
"Good Condition" is not desirable. Ideally, you a want a comic book to be in MINT or NEAR MINT condition. After that you want VERY FINE or FINE condition. After that you hope it would be in VERY GOOD condition. "Good" condition is actually near the bottom of the scale.
So yes, condition is important, as is the titles. Many of my comics are also from the ’60s and ’70s and some of these are only worth a few dollars each. However, my copy of Spider-Man #50, for example, in the condition I have it in, is worth about $700.00. Batman #200 is worth about $140.00.
Just GUESSING on the average true condition of your dad’s collection, and average titles, assuming your dad had 300, I would say it would cost him $1,200 - $2,100 to replace them. (The average worth of each one is probably in the $4.00 - $7.00 range.)
However, that’s not what he could sell them for, especially to a dealer. A dealer may only pay $500 for the entire lot, since the dealer has to make a profit when he tries to resell them. Maybe less, if the overall condition of the lot is poor, and if they consist of titles that are not popular.
Get me a list of the titles, and the true condition, and I can give you a better answer. Of course, you or your dad should purchase a copy of the latest Overstreet Comic Book Price Guide. It will tell you the value of each comic you have. It will also explain how to grade each comic.