Anywhere else!
Gw sell a novelty 'spray gun' that is shaped a bit like a flamer. Never even considered to try and use one as it just screams cheap from the look of the thing.
For a cheap airbrush there is a lot of Chinese made ones that will do a fine job of basecoating, and will last well enough if care is taken of them.
The higher end airbrushes (£100-200 and upwards) are often beautiful to use and the craftsmanship should show. But as far as usage goes they tend to shine through the crowd for freehand airbrush work, something which generally isnt done at warhammers scale.
http://www.ebay.co.uk/itm/Veda-Air-Brush-130A-airbrush-Model-Body-Paint-Tool-spray-Gun-/130869384051?pt=UK_Crafts_DrawingSupplies_EH&hash=item1e786c5373
This badboy comes in at a dirty cheap £14, And really ought to be fully capable of basecoats, zenithal highlighting and clear coats on 28mm miniatures. Some of the dearer ones might have noticeably better engineering or materials, which might mean things like smoother triggers, easier to clean and rebuild or longer life.
A hose shouldnt be more than £5-10, and a compresor... well get the best you can afford to, a spare car tire with the appropriate valve would be a decent cheap option, theres a huge range of compressors out there, an airbrush doesnt really need a very powerful air source, but does benefit from a tank (small one is good enough) to give the motor a break, allowing it to cool of a bit, and piston compressors are preferable to diaphragm ones due to 'pulsing' of the air. Oil free is preferable for cleaner air, but is noisier, oil cooled compressors can be used but filters and traps int he airline would be necessary.