the reason masters racers dope is because nobody tests masters, and nobody really cares if masters racers dope (except for the other competitors).
The race organiser does not pay for the testing directly. British Cycling takes a small levy for every rider taking part in a race and I imagine this goes towards paying for the random testing.
The UK anti-doping website has a list of all current and historical bans for drug test rule violations covering a wide range of sports:
https://www.ukad.org.uk/anti-doping-rule-violations/current-...