I made 1300 something and the hundreds of dollars are after I sell the rest of my comics which I'm being conservative about in how much I make on it.
I would suggest you look towards buying collections rather than a per book situation. Collections can include a wide range of books. From bulk loads of junk, runs, mild keys, $3-15 books and with luck there is always cream of the crop. Having outlets for your junk stuff is important. Sales threads, ebay and facebook to move the mid range and hopefully you got a presser to work with and a way to get better books graded. There is certainly more work involved but more profit if you buy it right and move it effectively.
+1 Chris
The "bread and butter" of this hobby/business (at least for me) has been buying 3-10 long box collections for a few hundred bucks and:
1) Putting a few nice keys into my collection/long term hold box
2) Selling remaining keys/semi-keys here and at shows
3) Dispersing the rest into my $1/$2/$3 show/antique mall boxes.
4) When the dollar boxes are burned out of decent books, sell them for $25 each.
Generally you can pay off the buy pretty quick with step 2, step 3 gets you longer term steady money. You can always sell a few step 1 books when you need to. There is really no way to lose on this formula. Your per book price is well under $1.
It's not as glamorous (or risky) as trying to flip a big (especially raw) book, but has worked for me for 40 years or so. I had been doing this for 35+ years before I dared to spend over $50 for a single book.