SP Purchases Map.
This is an entirely entity based hl2sp buy system. It would be better to make a mod for this. (Hammer crashes and all that rot).
You can buy weapons, ammo and equipment with points. The map starts you with points. You also get points for killing enemies. Go play around with it.
Mapmakers, use the clean copy and copy/paste (or prefab) everything into your map. I put the equipment camera box in the top forward side so the player can't hear the gunfire effect. The menu scanner needs info_air_nodes in order to navigate around in case the player gets out of its view. It will follow the player if it
sees the player again and a 10 second timer goes off, or the player gets close enough to the scanner. Info_air_nodes need to be placed around the map so the crow and pigeon can fly around and find enemies. Make enemies have an output onDeath that adds to map_counter, so that they add to points when they die. Look in the map for a building with a button. It unlocks a door and takes points off the counter, if you want purchasable doors or something, look at that as an example. If you want to add a buy option, look at how everything else was added in, its pretty complicated. Go on the hl2world irc channel, sometimes I'm on as much.