The most valuable coin on show will be a 1930 Australian "proof" penny, which is owned by a private collector and valued at more than $1 million. It is one of only six proof pennies made that year.

The weekend exhibition at the Brisbane Table Tennis Centre, hosted by the Australian Numismatic Dealers Association and Australian Philatelic Traders Association, has attracted dealers from around the country.

Melbourne-based dealer Belinda Downie has brought up the 1930 penny along with other rare coins including a "holey dollar" from 1813, one of the first Australian coins. Also in her collection is a 1824 Bank of NSW note of 20 Spanish Dollars.

The holey dollars can fetch upwards of $100,000 and the note is worth about $400,000, she said.

However Ms Downie says the $1 million penny always draws the most attention. The penny was never circulated because it was a proof (or collector) coin free of blemishes.

"There is a romantic notion to it," Ms Downie says.

"It was a coin struck during the depression when Australia was going through very tough times."

Modern-day proof coins from the Royal Australian Mint don't come cheap either. With only 100 made, a 2015 edition $2 coin will set you back $1450.

Ms Downie, whose business Coinworks sells a variety of rare coins and notes, said the entry market starts around the $3000 mark and the clients are varied.

"You'll have the plumber, the accountant, the top business people...it's not 'the surgeon' and 'the barrister'," she said.

"It appeals to a broad cross-section and there's a lot of parallels between our industry and the art industry."

She predicted a limited edition $2 coin to commemorate ANZAC Day - of which 1.5 million were made - and the first coins to feature a new monarch could be the collectors items for the future.

Unfortunately the chance of finding an rare collectable down the back of the couch or in the garden shed are very slim.

"These days with so much access to information on the internet people are pretty savvy. People, if they find something, they hit the computer straight away," Ms Downie said.