Thomas missed out on the same cash prize in Saturday's 400m at the Grand Prix final in Moscow, when Mark Richardson avenged his European Championship defeat by beating the Welshman into third place. But Thomas insisted he could aid the injury-ravaged British team's cause in South Africa by winning his individual event, as well as boosting his own bank balance.
"I'm going to win $50,000 in Johannesburg - I promise you that," said the 24-year-old European gold medallist.
Thomas will face American Jerome Young, who denied him an extra $10,000 by taking second place here, though both were given the same time of 44.96 seconds. "I was sure I got second place," said Thomas, who picked up $20,000. "It is a bit of a pain missing out on the extra cash, but I can make up for that in South Africa."
Richardson will now start favourite to win the Commonwealth crown after picking himself up from the confidence shattering defeat by Thomas in Hungary.
The 26-year-old from Windsor will head off to Malaysia in a few days to acclimatise, while his rival faces another 400m test in the World Cup - plus the relay - then a gruelling flight from Johannesburg.
"I want to do well in the Commonwealths to prove I am a championship runner," said Richardson, after finishing third in the Europeans.
Pulled out of meetings in Brussels, Berlin and Glasgow by his management as they restored his confidence on the training track, Richardson returned in style, with victory in 44.88 seconds.