Depends what you are looking for really.
Pretty much everyone on here will recommend buying something with a lid and the ability to have heat only in one part of the BBQ. If going with gas this would mean more than one burner, with charcoal then a kettle style BBQ is a good bet.
My choice at that money would be a Weber kettle like this
http://www.gardenxl.com/s/weber-57cm-on ... oduct.aspx although it's a tenner over your budget. Webers are good quality and it will last you years.
However there are many other brands of BBQ out there worth considering, just look for something that's good quality. When it comes to gas at that money, I can't really offer any advice, I'm not a gasser, but it is very convenient.