Hi Paul.
Until this summer - I used a Tamiya Spraywork.
It's a gun and compressor that runs off a 7.2 v battery.
I have 2 of them and still use one to spray RCS body prep onto shells before painting them.
If you can find one - it's a cheap, decent bit of kit to start with.
If I can find all the bits for my 2nd one you could have it for not much
Compressors are expensive - unless you want to wear ear defenders.
I treated myself to a Bambi and it's ace.
I've also bought various airbrushes off eBay - with varying results. A few have gone in the bin !
If you need anything let me know.
Oh - and practice on the inside of cut open pop bottles