It's risky because of Jagex catches one of your bots, chances are they'll ban all of them on the same IP. I don't think they'd ban your main account if you've NEVER botted, but you can never be sure these days.
You can buy a proxy here: http://osbot.org/forum/forum/178-other/ they're very easy to use, you just fill them in when you start the client and you're good to go. If you're looking to gold farm, you'll easily cover the cost of it. I've never heard of free VPNs/Proxies, but feel free to search the web for some, I wouldn't risk it though since others most likely have tried it too.
Hope that helps