Downgrading From Dedicated

At the moment I have a dedicated server with what used to be EV1. It's an HP P4 2Ghz with 1Gb RAM. I'm using 22Gb hard disk space but a lot of that is junk or system stuff that can be reduced. I'm typically using about 25Gb/month bandwidth but having spare would be important.

Now so far this is begging the question, 'why dedicated?'. It was because my site was taking very heavy usage in terms of PHP and MySQL, and it quickly outgrew the shared hosting it started on. Thing is, other than knowing it won't work on that, I don't know what it does need. I've been watching top for a little while and it's varying between 2 and 25% CPU, but this is hardly a scientific test. It (and free) also says I'm using nearly all my RAM, but that seems doubtful.

So, the first question - how can I determine my machine needs?

I think any new new VPS option has to be Linux. I'd go for unmanaged, but preferably with a control panel, only because I'm not experienced with setting up sites on Linux. The other things I need are multiple domains (I use my server as a DNS host ATM), IMAP, recent versions of MySQL & PHP etc, and SSH. Nothing too fancy.

I'm paying $150 at the moment. I'd think be looking at a budget of $30-50 but could be flexible on this. It has to be monthly in case I get this wrong, and has to be available to the UK.