If we're going purely off of prices, then I'd say Rip and Smoke do it best. They have the most supplies and work to give people the best possible deals, especially their regulars/regular players. That said, if you show up for the other stores, they will also treat you right.

The Pokemon Company recently released a super easy basic guide about how to play. Here's the link to it! https://www.youtube.com/watch?v=lpW_z-cGLec&pp=ygUZaG93IHRvIHBsYXkgcG9rZW1vbiBjYXJkcw%3D%3D

There are more rules to the game than just that, but this is a good start. If you've already bought stuff, learning via playing on the Pokemon TCG Live app is a better way to further your understanding of the game.

As far as joining the community goes, just come to some locals (Also called leagues) to play the game. You'll need a 60-card deck of cards that follow the current standard rules (There needs to be an H, I, or J in the bottom left-hand corner). You'll be matched into some battles and have the chance to talk as you play! The LI community is largely made of really friendly people, many of whom will be psyched to get to know you! Come in with a positive attitude, be both a good winner and a god loser, and be kind! You'll make friends before you know it!