buypainted is great, my younger brother is picking up a lot of tips from his videos (although I think is appalled at times by some of his habits
).
One of the nice things about the airbrush, is that you can buy coloured undercoats (Vallejo do a range of colours in 200ml bottls for about £11 a bottle), which means you can save a fortune on undercoat sprays, and potentially save a huge amount of time with some models (if you can use an undercoat that also acts as the base colour you build on, rather than starting at black/white, you can start at red/brown/green/grey).
Britmodeller.com has some good advice on airbrushes, paints and compressors for model work (and generally good all round for model talk and advice).
One important tip.
When you start using an Airbrush, invest in a proper mask, I paid about £30 for a good mask with replaceable filters (I think the mask was about £15 and the filters the same, I've yet to need to replace the filters).
We also bought a proper extractor for the spraying corner in the garage (about £250, new filters are about £20 every so often), which makes life much more pleasant, especially after undercoating a lot of models with rattle cans - where there used to be a visible miasma that would do a Nurgle greater daemon proud (and a nasty layer of spray dust when it settled), it keeps the air nice and clear
(you can barely smell the paint even without a mask).
[edit]
My spray area in the garage as it stands as of about March (I had just put in an ikea FREDRIK desk I picked up for £29 which is ideal for my spraying), I need to move the lights from where they were set for the old position on the left of the picture (a pair of 4 foot daylight tubes are just out of picture).
[edit2]
I think we spent about £400 on the H&S silverline 2in1, and compressor, then about the same again on extractor and other accessories, but you can pick up a cheap AB and compressor for about £80 (but may have issues with QC and getting spares), we went for a known quantity straight from the word go as we didn't want to muck around and I'm generally not one for buying cheap stuff if it's likely to get a lot of use.