I'm now hosting a blog on shared hosting(dreamhost). I'm very happy with that service. Now I want to create a forum for that. One of my friend told me to not to host forum on shared hosting, because it'll consume more resource and my account will be at rick of termination. So I'm looking for VPS hosting, My budget is 15-20 USD/month.
Just depends on how busy your forum will be. Most of the time, there are no issues with hosting a forum on a shared environment, unless your forum gets really, really busy. For your $15-20 budget, if that includes cPanel, you are not going to have an easy time finding something decent, since the cPanel license alone costs anywhere from $10-15. If you don't need a control panel, you should be able to find something very decent within your budget.
By the way, if you are very happy with Dreamhost, why not get a VPS with them? They aren't cheap by any means, but if you are happy with their service...
I find dreamhost VPSs overpriced and very limited. The "Full Root Access" is not really full root access and they impose some fairly fierce disk IO limits. I love their shared hosting but I am very underwhelmed by their VPSs when I tried them a few months ago after the price drop.
Our VPS are fast and affordable: http://www.cutehosting.com/vps-hosting/ You must give it a try. If you have any question related to our services, you may open up a ticket.