Your question is a bit confusing because you say you sit down with $500, but later you say "everyone folds to you with $300 behind," so I will address the question under both both stack sizes. Also, there are 2 key pieces of information you left out: how deep is everyone relative to villain, and what position you are in (I will assume you are in the BB based on the way this question was worded).
To answer this question you first have to understand villain's range in this spot. A typical MP open in 1/3 varies between 5% to 20% of hands depending on a multitude of factors, and is generally between 3BB to 5BB. In your case his open was 8BB, which is alarming.
My assumptions of villain in this scenario:
He is probably a recreational player, and is either really tight and playing 1 hand an hour, or is super loose and splashing around way too much.
Next you must analyze the most important piece of information you can get when sitting down at a new table, the stack sizes of all your opponents.
If most everyone at the table is $300 to $500 deep, then you are probably at a tight table, and should move on if you can. If you see that a few players have $300 stacks and the majority of players have $800+ stacks, then you immediately know who the whales are, and you can usually conclude that the short stacks are aggressive maniacs in the latter situation.
In your scenario, if all the other players had $1000+ dollars behind, and villain was the short stack with $600, you can safely snap call to his shove with the assumption that he is just a maniac.
Assuming that you don't have any pertinent stack sizing tells, here are my conclusions:
If you are only $300 deep (ie 100BB), you have to pay him off every time. Folding here to a complete unknown with no other reads would be a huge leak imo. The answers telling you to fold because villain's range is QQ+ are mathematically inaccurate. Even if you knew villain's range was precisely QQ+, AKo+, you are still priced in to call at this stack size.
This becomes a reluctant fold without any other knowledge. Villain's shove in this situation is awful for several reasons (which are out of scope for this question), so you should feel confident he will pay you eventually.
Since it is safe to assume villain is a req player, it would be preferable to either 3-bet to a really small size (something like $55) or just flat calling all together to avoid getting shoved on. In my experience, when facing a min 3-bet, bad players typically flat call all their decent hands, and 4-bet either QQ+ or KK+, which makes the rest of the hand play out in your favor. If villain shoves on you when you min 3-bet, you can safely fold since you are priced out (in both stack size scenarios).
Note that the latter approach is a terrible strategy against anyone resembling a decent player, and is purely an exploit on the fact that villain opened for 8BB.
This sort of question is based solely on assumptions you have to make in this situation. To make them effectively, you need to use equilab (or something similar). If you can't figure out how to use equilab, you can check out the Poker Bank. They are a (mostly) free poker training site and are a great resource for new players.