For encounter cards, I use: TitanShield
For player cards, I use these colored sleeves (I bought blue, orange, green, purple, and red): BCW Elite 2
The investigator card sleeves are showing a bit of wear after playing 5 campaigns with them (fronts getting a bit cloudy). But the TitanShield sleeves work GREAT for the encounter cards.
I can get 600 sleeves for ~$44, so not much better than what you're asking but in the end I'll be paying less by having my cards protected. I like these because the one textured side makes shuffling these easier. Really solid quality for sleeves. I've purchased various brands but these I was happiest with quality/cost ratio.
If you're looking for cheap than going with what has been said penny sleeves are cheap and not great as far as sleeve quality goes but it's still better than nothing. Here's 500 for $12.
For scenario cards, I use TitanShield premium clear card sleeves. They have a matte finish on one side.
For investigator cards, I use Dragon Shield classic clear sleeves. As these ones are a bit more pricey, the only cards I keep sleeved at all times are weaknesses, and cards that are part of scenarios. I have a pack of 100 sleeves that I will use for whatever investigator cards I am using at the time, and I will unsleeve them when I am finished.
I use these sleeves
Fit pretty well and the little extra room allows me to get them out easily without ruining the sleeve in the process. Also withstands aggressive shuffling well.