Guys, the issue isn't the cost. The problem is my server host. And not because they are no good, more that they just don't offer a package with enough space. I was letting people attach images, but the images folder is now over 500Mb of my 1000Mb limit. Given there are so many image hosting sites around, I figured it was better to stop that and let people post their images on one of those and just link it in. The other option is to go offshore and use a US hosting service which has a lot more space for a lot less money. I can't add space to my existing setup cos I don't own the server, I just rent a package off them. I am no IT guru!
I've been thinking about going to one of these other hosting services, but the hassle of setting up the site there and migrating the domain and so on has stopped me doing it, but maybe it's worth thinking about in some way... I'll have to give it some thought.