Agreed - $40k is too little to contemplate setting up a SMSF.
Because a SMSF has to contribute a 20% deposit towards the property price, plus pay stamp duty, buying costs (eg building and pest inspection), bank fees (can be around $2500) and bare trust setup fees, the SMSF would be able to afford a property priced at $140k at a push. Such a property would yield only around $6k (in rent) per year, and a good third of that would get chewed up in annual accounting fees, death and TPD insurances for you, and ASIC fees.
I can't see any sense in setting up a SMSF unless it has $70k at a minimum. It must also be remembered that if a SMSF is setup and all it does is buy one property, then it will not be able to support its member(s) in retirement (unless it is one heck of a high yielding property). As such, if a SMSF setup with just $70k and purchased a property, you would want to be sure you could be bucketing money into the SMSF with a view to it purchasing its second property within say, 3 years. This is why Terry mentioned it is best if there is $150k+. That way the SMSF could set up, and buy two houses straight away.
Everyone's circumstance is different... everyone's income level is different, age proximity to retirement is different, family setup and financial challenges are different. It is for this reason it is always strongly encouraged that someone pondering an SMSF chats it over with a financial advisor first. With that said, many still have little or no exposure to the power of purchasing property with super and are thus by default saying "Oh no, no no no, bad idea". Sometimes you have to hunt around and talk to a few folks and ask "Why?" "Why is it a good/bad idea?" And incorporate your own thoughts and rationale into concluding what is best for you.
Things to remember if you are keen on SMSF: you can "share" a SMSF with someone such as your wife. The SMSF can have up to 4 members. You can "donate" money into your SMSF to help give it a head start.