You can actually get friends on steam without payments. They need to add you. But unfortunately you won’t be able to chat with them until you (bought) and activated your first game.
But. There are numerous sites, for example www.tremorgames.com [spoiler]Not advertising, just wanna help the guy so he don’t need to spend money[/spoiler] and others. Play some bad puzzle flash games for achievements and redeem a cheap-ass game for 99 upwards points. Wait a day or 2 for the key, activate it in steam. The system marks you as a non-freeloader and you can add friends.
If that somehow doesn’t work and you actually need to buy a game from steam store and not just activating a steam game key, then you can spend money on a steam gift card. But I would try the free method first. I mean, it’s just for the friend function.