The charity event at Melbourne's Rod Laver Arena on September 20 sold out within hours of going on sale Tuesday, with premium tickets priced at $1650.
Fans complained online of waiting in virtual queues of more than 30,000 customers only to miss out on tickets, while others described the pricing as atrocious.
"Sorry but the prices were ridiculous, $1700 a ticket is outrageous," said one Farnham fan.
Others speculated the singer himself would not approve of the situation.
"He would not be pleased with the pricing of this concert. Only the privileged few could afford to attend... it was appalling the way the ticketing has been handled."
The cheapest seats were priced at $179 and disappeared within minutes, according to fans.
"The excitement surrounding this special event reflects the enormous love Australians have for John Farnham and his music," concert organisers said in an online statement.
Ticket sales were run by Ticketek Australia, which warned customers to be aware that prices could change.
"Please be aware the price of a ticket for this event may increase or decrease at any time," it said in an online pop-up message to hopeful ticket buyers.
The concert is being held to raise funds for Head and Neck Cancer Australia, which supported the much-loved singer when he was diagnosed with a cancerous tumour in his mouth.
Farnham underwent a 12 hour operation to remove the growth in 2022 and has since been given the all-clear by his medical team.
The concert is expected to make a significant contribution to supporting Australians affected by these types of cancers, the charity told AAP.
But it has distanced itself from pricing for the event.
The income and costs are being handled by the promoter, according to Head and Neck Cancer Australia chief executive Nadia Rosin, with net proceeds donated to the charity.
"Ticketing and pricing for the concert - including the use of dynamic pricing - are managed independently by the event promoter and ticketing provider," she said in a statement.
"We recognise that ticket pricing is an important issue, particularly given the level of public interest in this event," she said.
Surge pricing, otherwise known as dynamic pricing, is not illegal but businesses must be clear about the price consumers will pay, according to consumer watchdog the ACCC.
Dynamic pricing for big-name international touring acts such as Green Day has previously disappointed Australian fans, while other bands such as Oasis have declined to use the pricing mechanism.
Farnham himself won't be performing at the tribute show, which will feature big-name acts such as Jimmy Barnes, Tina Arena, Human Nature, Keith Urban and Jessica Mauboy.
The concert is being run with the support of the Victorian government.
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