Tickets for the gig at Melbourne's Rod Laver Arena on September 20 went on sale on Tuesday, with the cheapest available seats priced at $179 by the evening and many more on sale for about $1000.
Farnham fans trying to buy tickets online have complained on social media about long virtual queues and having to pay more for expensive seats.
"Wow, who can afford that?" commented one Farnham fan online, while another described the cost as an absolute joke.
"Looks like dynamic pricing will be happening, which is awful considering it is a charity event," said another.
Farnham himself won't be performing at the gig, which is being held to raise funds for Head and Neck Cancer Australia.
"This night isn't about me — it's about giving something back and supporting a cause that means a great deal to me," he said when the concert was announced on Friday.
Head and Neck Cancer Australia has supported the star, who retired from public life after undergoing a 12-hour operation to remove a cancerous tumour from his mouth in 2022.
He has since been given the all-clear by his medical team.
The use of 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.
Ticket sales for the Farnham tribute show are being run by Ticketek Australia, which has told customers to be aware that prices could increase or decrease at any time.
The concert is being staged with the support of the Victorian government, and the state's Minister for Sport and Major Events Steve Dimopoulos has predicted an economic boost from the one-night-only performance.
Jimmy Barnes, Tina Arena, Human Nature, Keith Urban and Jessica Mauboy are among the names slated to appear.
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