Don't buy from a store - you'll be overcharged and the beardie is FAR less likely to have had as good a start in life as it would have done in the hands of a reputable private breeder.
I've lost count of the times that I've seen baby beardies (well, actually all manner of reptiles) kept in totally inappropriate conditions, without the appropriate UVB lighting (absolutely vital for bearded dragons to synthesise vitD3, that then allows then to metabolise calcium) and being fed terrible diets, and kept on substrates that are known to cause impaction if ingested.
As a first port of call, I'd recommend having a look at www.reptileforums.co.uk/forums/lizard-classifieds/ for the beardie, and www.reptileforums.co.uk/forums/equipment-classifieds/ for quality used equipment for a fraction of the price of new.
For lighting you will either need a UVB tube these are perfect, and a separate basking/heat lamp (standard incandescent bulb - although not sure if you can buy them any more in the UK??) or an all in one heat and UVB bulb (a mercury vapour bulb) which are also available from Darren at Kimbo's Reptile World www.kimbosreptileworld.co.uk/mega-120w-self-ballasted-p-143.html
You might be correct in that beardies are pretty low maintenance once you have the setup just right, but they are far from cheap, so I don't know if that's a consideration? Those expensive lights need changing every 6-12 months as their UVB output drops over time. They need their vivarium kept warm at all times (unless you are actively trying to brumate the B.D.) and they must have access to a basking spot of around 38C-40C to effectively digest their food. Also a baby beardie can eat 40-60 tiny crickets per day, which is not cheap unless you breed your own! Also, in reference to AwayWithTheFaries mention of a 3' viv - that will not last a bearded dragon to adulthood (well, not humanely, anyway, so do be prepared for how much space their environment will eventually have to take up in your home.
Sorry to sound so negative. Beardies are fabulous pets! I just know of many people who have bought them without knowing what they're taking on, and the beardies have ended up unwanted or unwell as a result.