Hi Catherine, and "Welcome!"
First bit of advice is to think about how you want to use your van, because that will narrow down your choice.
If it's to be your sole vehicle, you'll want something smaller than if it's just for the time you spend away in it.
If you plan to do long holidays (a month or more at a time) you'll need a lot more space than if you only want to do weekend/week/fortnight trips - and may want fixed beds rather than ones which use the seats.
If you only ever plan to stay on fully-equipped campsites, you won't need as much in the way of onboard facilties as you will if you want to wild-camp in the UK, or use Aires on the continent.
If most of its mileage will be on continental trips, you might even want to see if you can get a lefthand drive van!
So talk some of those questions over together, then look around at some dealerships (and maybe shows) to see what sort of size and layout will suit you best. Your budget means you'll be looking at older vehicles than most of the ones at shows or on dealers' forecourts, but you'll get some idea of what you're looking for when you start following up (mostly private) ads for vans in your price-range. Don't be put off by age or mileage, as neither of those things matters much on a motorhome if it's been well looked-after.
Once you're a bit clearer about what you'll need, post some more detail on here and you'll no doubt get some suggestions as to makes and models.
Hope that helps - enjoy your search!