Are any of you baseball card dealers???

Last week I stumbled upon a whole bunch of cards at the thrift shop. It looked like a dealer or collector had unloaded a collection. I didn't buy any of the stuff on the shelves that was normally priced because I know zip about baseball cards. But I did happen upon the "quarter shelf" area that had a promo going to fill a bag for a dollar. I spotted a bunch of baseball cards nicely protected in vinyl slots in binder-style pages. There were probably a total of a couple hundred cards, mostly from the years 1987 through 2000. I assumed they were crap, then I noticed whoever had them put little notes in some of them, mostly "RC" which I quickly discovered meant "rookie card." So I dragged them home for a dollar and looked some of them up on ebay. I nearly fell off my chair when the third one I looked up had sold, graded, for over $500. I found lots of cards in the $10 to $30 range and one for $300+ and I haven't even checked half of them. My question is about grading. Is this difficult to get done? I checked a couple sites of grading companies - PSA and Beckett - and I couldn't even figure out how you submit the cards. I can't decide if I should invest money in these things and try to sell them myself or just find a dealer to take them off my hands since I paid so little for them. Opinions??