Sheldon J, I would doubt today you would find a 15 year old comic in a mylar bag for .30 cents. The mylar bag alone is worth at least a quarter alone, and if the backboard is acid free, add a few more cents.. Unfortunately most comics from the mid 80's and up aren't worth a whole lot to begin with. The comics worth the good money are basically from the 50's through the early 70's. Yeah the older comics from the late 30's & 40's are a great find, but I wouldn't shell out the money for them.
In the early years of my collecting I started out with most of the popular titles of the time and boy do I wish I had half of what I got rid of today.
I only kept a good portion of my older Marvel collection. ASM, Thor, X-Men, FF 4, Avengers, virtually every Marvel title to be honest.. The 60's and 70's had many key issues and for the most part I was able to recognize some and buy multiples on it

Even in the 80's I saw a few that I think were good deals. Found a store the was selling a trade paperback of Batman's the Killing Joke for $2.50 I bought 10 of them

Although comic prices rise and fall, last time I looked it was going for about $28.
hombre_de_plata_flaco, had those old Horror magazines too, that and the True Crime magazines.
I had 2 favorite shops where I could buy the used comics for a fraction of their cost. This was before people realized they could make some sweet money on it.. I would love to find some of the old comics now at a decent price.
Even at the flea markets, any cheap comic is an off brand, or non popular title. Some think because the comic is over 10 years old it has value. I have seen people trying to get top dollar for a comic with a poor artist just due to the age.

You want to do well, know your artist and writer combos to make a few bucks.