Disposable plastic pipettes are great for mixing paint and dispensing thinner. Testors sells plastic pipettes in boxes of 4 or 5 for less than $10.
At eBay for less than $10 you can get a box of 500 or 1000! I just purchased 500 very nice pipettes which are graduated so I can measure out exact ratios.
eBay sellers also offer all kinds of little bottles and other capped containers that could be useful for mixing and thinning paint prior to airbrushing. I never have enough of those despite scavenging paint bottles as soon as the paint is used up.
Happy eBaying!