Minecraft – Play Minecraft Classic Server when Minecraft.net is down

The wiki has an excellent guide to configuring your first server.

Configuring the Minecraft Server

1. Configure the server by editing the server.properties file, the format for which is explained here. Be certain to edit the file with a text editor that does not add formatting (e.g., for italics). Additional configuration may not be necessary as many servers run fine from the default values.

2. Add your username to the admin.txt and/or ops.txt (newer Minecraft versions may not have an admin.txt file).

   • Ops.txt and admin.txt determine who may execute server commands. In other words, operator ("op") privileges allow you to control certain aspects of the game (e.g., teleporting players).

   • Op privileges may also be granted from the server GUI: type "op " and it will automatically add to the ops.txt file. Being an op will not let you fly and/or have a creative inventory

I don't think you quite understand Minecraft's business model.

Minecraft checks in with Minecraft.net as a rudimentary form of DRM - if you can't log in, you don't have an account with the site; if you haven't bought an account with the site, you haven't bought the game. It's a little bit like Starcraft 2 in that respect - you must log in to your online account in order to play the game, even in single player.

It's been that way since the first for-pay version of Minecraft, before multiplayer was even a feature. It's literally just a quick "do you actually own the game" check, nothing more.

It's also not a subscription. You pay for the game once, and then the account with which you purchased the game can download it from the website. There is no recurring fee.

TL;DR: You do just purchase and download the .jar files.